The 6502 had special support for BCD arithmetic, because it was widely used in those days; this much, it had in common with other CPUs.
But the 8080 and 6800 implemented this in the form of a 'decimal adjust after addition' instruction, the idea being that to add two pairs of BCD digits, you first of all add the bytes using the ordinary binary add instruction, which also sets half and full carry flags from four and eight bits respectively, then DAA checks the results and the flags and performs a fixup to make them correct for a BCD add.
Yet the 6502, designed by some of the inventors of the 6800, takes a different strategy; it provides a BCD mode, as a global flag which when set, causes all addition and subtraction to give the correct results for BCD until cleared.
This seems intuitively like a 'higher level' design, one that does more work for the programmer in order to more closely match intuition. That is particularly surprising because generally speaking the 6502 was a simpler processor that skimped on programmer comfort for the sake of lower cost.
Why did the 6502 designers choose this way of handling BCD? Was there some lesson learned after the 6800, some reason they figured this was the right way to do it after all?