They kinda hit a standstill on the networking side as they moved to the trash can Mac, and I think that had killed momentum towards any high speed IO besides the Thunderbolt ports moving forward.
I was hopeful they'd keep the Mac Pro going into the M-series era but after one version... it's gone.
So, it seems that Tim Cook decided at some point that while it's nice to make $5,000 in profit from a Mac Pro sale every day or two (okay, I kid, I'm sure they sell a bit more than 365 a year), even if they hang those "pros" out to dry completely and they defect to Windows, Apple would be better off spending their time focusing on ways to make the MacBook Air and Neo more attractive or profitable because they move orders of magnitude more units of those.
Note: I don't like this, but my feelings have nothing to do with it, I think it's just a classic Tim Cook Numbers-first business decision