I think your conjecture about being stomped on is likely the culprit in most cases. The QRM levels on FT8 when the bands are open seem much worse than I have experienced on CW or SSB (with the exception of perhaps some major phone contests). And it's exacerbated by those who don't check their waterfall carefully to find an open frequency before transmitting.
I have found that incomplete QSOs are much more common on FT8 than analog modes. On the other hand, my minimal antennas are enough to work dx that just wouldn't be able to hear me on ssb, or even cw. So there's a trade-off.
Due to the popularity of FT8, there really is a need for more bandwidth for this mode. But that takes delicate negotiations and changes in operating practices.