There'd be little material value in grabbing-for-recycling (or other re-use, etc) non-working sats or
bits of sats. No more than visiting your local scrapyard in constructing your new Hubble/whatever. (Almost anything usefully prefabricated could probably just be re-fabricated from scratch better. Unless you used you last half kilo of Unobtanium-13 in the original item, maybe, but that's not gonna be the case this side of a dreadfully-laboured film plot.)
And some objects up there, with military/intelligence missions to them, might be designed to
not to be captured, and their owners not look kindly on non-owners potentially retrieving any bits.
The big need is to just stop the bits floating around out there (without any hope or need to get them home). Sooner than later, ideally, before it gets to the point where they're unmanagably numerous.
Of course, sending rockets up with things on them that can get other bits down is tricky enough, and you don't want to risk adding to the problem (your garbage-collector hitting other things badly, breaking so that it becomes garbage, leaving its own extra bits like rocket-fairings that reach orbital heights), and you're having to spend money on a launch that
isn't adding communications, space-telescopy, supplies to spacemen, etc. So it has to be a harder sell. Luckily, some people take the Kessler thing seriously (as others did viral epidemics, so that might be scant reassurance).
Oh, and unless you're Wile E. Coyote, you generally can't hold a magnet out in the direction of a distant object and have it magically zoom towards you (usually including unforeseen things like stray airliners and mysterious anvils, as well as the ball-bearings that you previously hid in amongst the pile of birdfeed). Anything on Earth that could reach up magnetically to orbit and usefully help (with the Nickel, Iron, Cobalt or Steel bits, unless you can induce complimentary electromagnetism in other conductors as well, which is a thing in, e.g., aluminium sorting and recycling) is
probably very much weaponisable here on Earth so not casually available for orbital cleaners to play around with.
Hence why it's still a very much embryonic concept, loads of ideas that are very rough and ready but no definite answers yet. The best current idea, in use, is just to try to make sure any sat you send up has a 'death reserve' of propellant, and the wherewithall to use it as your final act of control, to make sure the thing can be pushed down/up[1] and somewhere it is safer.
[1] As KSP players will know, it's not really those, but let's say it is to save time, eh?