They're not losing it, just an approach in search for a different one. The music always is more than the notes, it also encompasses the sound, and that is linked to instruments. Cellos or violins in Bach's time sounded different, that's a fact. The introduction of steel strings and higher tension and modern tunings changes the sound a lot.
Like Skip Sempé stated:
"In most fine music written before the 1950s, the sound and the composition were linked by the composer. Some performers do not care about this, and some listeners don't care either, but that was clearly the method behind the tradition in question. Without any doubt, this is the manner in which harpsichord music was conceived."
I appreciate the approach of a lot of these players, but I just can't get around to like their sound.
"These players" being the non-HIP, what some would call "romantic" performers, I assume, or am I misunderstanding what you're saying? I tend to agree with that, though for me it's not a "black and white" case.