A technical résumé, to a non-technical recruiter, is just technobabble; they have no way of knowing whether the information contained in the résumé is generally good, or just someone BS'ing, or someone who doesn't know what they're talking about. Discerning whether a writer actually understands what they're talking about (particularly in the terse format of a résumé) generally requires a deeper understanding of the lexicon at hand.
They can be told to look for certain keywords, sure, but that doesn't, IME, seem to be sufficient to screen; obviously bad résumé use the right words (but in the wrong ways / in ways that to an expert clearly indicate a lack of understanding) so they pass the filter.
Brief technical screens can be done, but again, without technical knowledge, the recruiter can't know if the answer given by the candidate matches the answer they have in an answer key, if they are provided with one. Even relatively simple technical questions might have more than one right answer, or the answer might just be phrased in a way that a recruiter doing a human version of lexical edit distance isn't going to think passes, but any engineer would say would.
The problem in all of these is the lack of technical knowledge. Tech recruiters, on the whole IME, are trying to recruiter for a role that might as well be "town wizard". Any theoretical recruiter with technical knowledge would never work in recruiting — they'd fetch more in pretty much any real technical role, like an engineering role.¹
The other problem, again IME, is that there is a wide pool of candidates with very little actual experience, though they may have worked any number of years. Finding someone with actual knowledge and understanding of software engineering requires sifting through a lot of chaff.
¹One might see this as people aren't willing to sufficiently pay enough for recruiters / if you want a recruiter with technical knowledge, you need to compensate them adequately enough that other opportunities are not worth their time. I would agree here.