I can relate to this.
(I originally went on to describe lane-courtesy (especially non-nearside "overtaking"), junction filtering (with particular reference to letting people "slot on") and behaviour in depressed-speed multi-lane situations (on approach to bottlenecks, real or phantom), as it applies to the UK (both as it should apply, and how it applies in practice due to drivers with different approaches to attentiveness, considerateness, etiquette and possibly even knowledge of the rules). I got into double-digits of feetnete, and many heartfelt paragraphs. - Decided you didn't want all that, just deleted all of it! Starting again...)
...twice, yesterday, the following setup occured:
Three-lane motorway, am on the nearside, comfortably behind another vehicle (comfortably behind at least one more, in front), at maybe 65mph (national speed limit is 70mph, and obviously applies to this road, but 60-65mph was a reasonable speed to go - fast enough for purpose, road conditions actually better then than earlier and (probably) right now). Nothing sitting behind me (for quite some distance, anyway) and nothing in middle/offside lanes. Junction filters in, long sliproad, vehicle obliquely visible in mirror, initially well behind me. Obvious thing for it to do is to filter on behind me. If it wants to go faster (say 70mph, 'cos... you know, speed limit... yeahIknow!), easy to do so, plenty of vision all around, etc.
What happened:
Onfiltering vehicle sped up to barely make it beyond me, in the rapidly narrowing sliproad triangle, to edge between me and the vehicle in front. (Instead of me a close-but-comfortable distance behind that, now I've got a car/van uncomfortably close to it and I'm uncomfortably close to them ...even with a touch of brakes.) For a fraction of a second, at least, as they then pull out into the next lane over and zoom off at (at least!) NSL+10mph.
They both could have held off (or at least not gone full Mad Max in attaining motorway speeds), edged on behind me, continued to edge over to pass me (and the rest) and done what they wanted from there on in. Saved seconds, maybe, but unnecessarily risking at least two vehicles' safety (including their own), definitely.
(And never saw any indicators being used, either.)