Many of us hold nostalgic affinity for the M77’s, myself included, but the lack of aftermarket support, the sloppy action feel, and challenging accuracy compared to many other actions have been self limiting.
There are also a lot of rumors flying around by relatively poor quality shadetree gunsmiths regarding the cast receivers - I’ve heard it all, “you can’t remove the barrels without risking cracking the brittle receivers,” or “you can’t blueprint them because the cast receivers are surface hardened too hard.” Even further, the angled forward action screw has been used as an excuse by many smiths who claim they can’t be blocked and bedded. Of course, most of these are excuses to bypass uncommon work rather than building or buying fixtures which won’t be as productive as more common models, or taking extra time to do multi-step bedding jobs. If a guy can keep the lights on with Rem 700 work, why waste time and money on fixtures for a rifle which comes across the bench once every three or four years?