Lack of manager ability to measure productivity based on anything else. Between POs, BAs, business representatives, and IT managers there are a lot of people who don't seem to be able to grasp why two relatively simple to describe tasks can require such vast differences in time. So it becomes hard for them to judge if their developer is wasting their time or not (and let's not even begin on overall lack of trust to begin with), so the only fall back measure is if they have their butt in the seat and appear to be working. And even if you are lucky enough that everyone you directly deal with either understands the basics on why sizing varies so greatly or able to accept it without question, you still have to deal with middle managers walking the floor who measure productivity the same as they would in a factory. And if you are lucky enough to not even have this problems, you still have to deal with cultural norms set in party by all the jobs which aren't as lucky.