Motorola wanted to replace the 68000 series with their RISC design, the 88000, so it was probably always going to end there. Their customers were also all in full RISC hype fever and were looking for RISC chips to move to.
In Apple's search for a RISC chip, didn't want to be stuck being single-sourced again so they had IBM and Motorola work together to launch PowerPC instead, so Motorola gave up on the 88k.
I have seen mentioned a couple of times that the 88K would have had some inherent design flaw that made the architecture a dead end. I have never found an explanation what that would have been though.
Perhaps this had just been a misunderstanding of a second-hand statement. Its first iteration was flawed in that it was an expensive multi-chip solution with few buyers. The second was more integrated though.
My understanding is that by the time the second iteration came around, the AIM Alliance had been formed and Motorola simply abandoned the 88k and started focusing on PowerPC.
If NeXT hadn’t killed their hardware division in 93, the RISC Workstation would’ve run an MC88110.