I don't know where you're getting your information, but it's not very accurate. Torpedoes were popular, ORIGINALLY, because they were seen as a way for "underdog" navies to counter the superpowers. Namely, the Royal Navy. And when I say originally, I mean "for the first five years after the torpedo was invented". This obviously wasn't the case, the torpedo isn't a superweapon. It is, however, a very powerful and useful device when employed properly, hence why everybody and their brother's second cousin adopted the things.
Large numbers, of course. SO WERE NAVAL GUNS. WWI hit ratios were HUNDREDS of shots fired PER HIT. Torpedo hit ratios might have been BETTER, simply because fewer torpedoes were employed and they did score hits. Actually, heck, I've got a book that notes the number of torpedoes fired and hits at Jutland, as well as the ammunition expenditure per hit for standard naval guns.
Capital ship shells fired:
4480 British, 3574 German
HITS:
102 British, 85 German
2.27% hit rate for British guns, 2.37% hit rate for German guns
Torpedoes fired:
94 British, 105 German
HITS:
6 British, 3 German (one disputed, so possibly two)
6.38% hit rate British, 2.85% German
And darn, would you look at that? The *torpedo* is more accurate than the standard capital ship naval gun. I will also note that during various other smaller engagements the British had the fantastic achievement of having a small cruiser squadron IIRC empty their entire magazines without scoring a single hit. In Tsushima, the Russo-Japanese War engagement you're undoubtedly thinking of as it's the most famous, the hit rates were not any better. In fact, they were probably worse, since both sides were using equipment that wasn't up-to-date and they weren't trained up to the level of the Royal Navy or anything. Also the Japanese followed the philosophy of "if you fire enough you will score hits" which made the Russian gunnery in the initial long-range stages of the battle substantially more accurate, until the range came down and the Japanese started scoring more hits. Not many more compared to the number of shots fired, mind you.
Evasive action: Battleships require minutes and miles to make a turn. Firing torpedoes at them stands a great chance of getting hits, hence why TBDs/screening forces exist. "Up close" is at approximately the range of a light gun such as may be found as a destroyer's main armament, in fact.
Premature explosions? When? What? Sources? Please? Something? Torpedoes don't randomly go off in the water. I mean, maybe with the faulty magnetic pistols, but even then, they were mostly known for NOT going off when they should've.
Torpedo boats worked by being fast and hard to hit, which is fairly effective so long as you don't get, say, a squadron of destroyers sticking itself between your MTBs and their targets and filling the ocean with automatic cannon fire or quick-firing artillery shells. As for battleships being designed to take such hits...underwater protection (protection against torpedoes) is generally only enough to stop the ship from sinking immediately right now. Ships that get torpedoed are ALWAYS in deep trouble, and are forced to heel out of line since they can no longer make speed...which leaves them vulnerable to more accurate fire as they're no longer moving as fast. ALSO: Battleships are NOT designed to operate with massive holes in them. Battleship armor is designed around "keep the exploding devices outside my ship". Torpedo defenses are focused on the destroyers, which should, ideally, DESTROY torpedo-armed craft before they can get close enough to shoot at the extremely vulnerable battleships.
----Special mention goes to the German battlecruiser Lutzow, which got torpedoed and lost its entire bow, but just kept right along steaming, keeping up with the rest of the fleet, until the bow was seventy feet down and the propellers were out of the water. This is pretty darned impressive survivability for even a battleship. German ships were always notably tougher than most.
A ship, even a small one, could carry more than four torpedoes in the immediate pre-WWI era. The sizes of TBDs (torpedo boat destroyers, what you'd recognize as a WWI/WWII destroyer) had been steadily growing, and their armaments were VERY eclectic. Some ships went for gun armament, some for more torpedoes. Some torpedo-light but gun-heavy ships might have carried only two dual launchers on deck (usually with reloads, though reloading torpedoes is almost never done in battle as far as I'm aware), but some of the torpedo-heavy ships could carry many, MANY more. For instance, the US' WWI-era Clemson class destroyers (And the three or four nearly identical classes that preceded it) carried four triple launchers, with a decent gun armament as well.
As for the Russian flagship: yeah, the entire superstructure was basically gone. Yeah, the ship was settling fast. Yeah, it was entirely on fire. Yeah, all the main guns were disabled. But the secondary batteries and other weapons were STILL FIRING. Nobody is going to take their MTB into point-blank range to guarantee a hit on the DRIFTING (not stationary) hulk when they might get hit and explode for their trouble.
You do indeed need to take speeds, weather conditions, distances, and all that for torpedoes. You also needed to take all of those into account for your own main battery...and you ended up being basically just as likely to score a hit with a torpedo as you were with a main gun, with the added benefits of missed torpedoes forcing the enemy to turn and run from the incoming torpedoes, thus making them very vulnerable.