Hugh Aguilar wrote:
[..]--- the 6800 was pretty much obsolete from day one; it never got used much for anything.
While I agree about the 6800 being cumbersome in some respects, it was still used, not only in the Altair 680B or the SWTPC (checking Wikipedia: Also the Tektronix 4051 computer). But maybe the derivatives of the 6800 is where the real use was. The TU80 and TU81 (DEC tape drives) I remember from the top of my head. They used the 6802 variant, with 128 bytes of built-in RAM. I've also seen the 6800 original used in other peripherals here and there. So the 6800 family (leaving out the real fix - the 6809) ended up mainly in the market Chuck Peddle had in mind for the 6502, he apparently didn't imagine a personal computer revolution involving the 6502. As for the 6800, even though it's no 6502, I suspect that the total number of 6800-compatible CPUs sold over the years was quite large. The legacy of the 6800 (and its support chips) shouldn't be underestimated. The 1-index register variant managed to live on as the 68HC05 for some time, although the 68HC11 did better (and is still used) with two index registers (but otherwise instruction compatible with the 6800).
The 6501/6502 was all about saving silicon, to be able to sell the chip at less than a tenth of the going price for CPUs at the time ($360 according to Wikipedia). Motorola didn't believe in that approach, which is why Peddle&Co left. So the design choices for the 6501/6502 was more about saving silicon, and doing the best of what was left, than about an optimal design seen from a programmer's point of view. But they did put some effort into getting very fast interrupts, and all in all I think the 6502 did exceedingly well with what could be done with the available silicon.
As for compilers, remember that FORTRAN (and COBOL!) had been around since the fifties, and you could run FORTRAN in 4K on late sixties/early seventies minis. So maybe the memory cost wasn't really why the CPU wasn't designed for compilers (if that was indeed the case), but maybe more the PDP-11 idea[*] - that it should be easy, or even delightful, to program in assembly code.
[*](Although there were earlier architectures with a similar idea, just not as well known as the PDP-11)