It is also quite easy to get wrong, because you need to null the offset of the op amp and only the op amp itself. The offset voltage drift is (first order wise) proportional to static offset voltage, so if you null the circuit, and not the op amp, you can get tempcos that are far worse than almost any op amp with no nulling. After a certain point this also has an impact on linearity errors, i.e. distortion increases.
(The exact implications of the offset null depends on the nulling scheme in the op amp: most use a 741-style adjustment)
Last but not least what c4757p said: besides the fact that a correct offset null can be difficult or impossible in some circuits it is also a manual labor step that can take a good while and is simply not compatible with time + cost requirements in modern fabrication.
'Modern' fab processes are much improved, so you get much better precision and a much lower price point: The fabrication is better, so better un-trimmed accuracy, plus faster (=cheaper) and more accurate wafer trimming.
A completely different story are compensation pins. These can be quite handy, because they can also be used as a strobe input in many op amps. These mostly went out the window because most op amps are dual in SO-8 or smaller packages and there just ain't enough pins for that.