Like, for example, only one external interrupt and one timer, which was 8-bit.
I did some reverse engineering on an 80s Porsche engine management computer[1] that used the 8048. The engineers had to get really clever to work with these 2 issues. They used the reset pin as a second pseudo ext interrupt, which works ok but has a few side effects you have to deal with.
The lack of a 16 bit timer was single-handedly responsible for adding massive complexity all over the code. Basically the loops had to be capable of scaling themselves for engine speeds below a certain threshold because otherwise the timer would overflow!
You have to wonder if it was worth what they saved vs just using an 8051, especially considering that this car had 2 engine management computers, and the main one used an 8051!