The on-chip stack on the 6502 was not intended to be used for implementing the stack for programming language procedure calls; it was intended to provide system

The on-chip stack on the 6502 was not intended to be used for implementing the stack for programming language procedure calls; it was intended to provide system extension functions that provide things missing in the 6502 instruction set,(for example, multiply), which had to be implemented with multiple instructions. For "modern" languages like C, 16-bit 2's complement integer arithmetic was expected but the 6502 native instructions were for 8-bit numbers.