[userbinator]

A lot of newer CPUs aren't available in DIP packaging which means they won't be usable with a breadboard; the M68k is one of the more unusual ones in that it's available in a 64-pin DIP, the longest common DIP package. E.g. all the x86 processors moved to square packages starting with the 80186/80188, only the 8086/8088 were in DIP.

DIP packages are problematic for high-speed operation since the leads to the pins near the ends are longer than the ones in the middle, creating signal skew; hence the move to square/BGA packages.

That being said, there are microcontrollers with a relatively powerful ARM core and in DIP, but they usually have internal memory and use the pins for peripherals, not as a full memory data/address bus.

[Narishma]

A lot? Make that pretty much all. The only things you still find in DIP format are very low-end micro-controllers.

[kjs3]

Not ARM microcontrollers, which the OP specifically references. NXP’s LPC810 & LPC1114 are really the only game there, and they don't support external memory AFAIK (and it's an M0). Of course, there are a lot of shops bonding an QFP ARM or similar to a slip of PCB that's DIP form factor, but that's not exactly the same.