Many people misunderstand and think that trans women conforming to gender roles are reinforcing stereotypes. Simultaneously if a trans woman does not embody the stereotype of the 'ideal' woman then she is not actually 'trying' and not a 'real' woman. Similar examples exist for trans men I am sure. Many people seem to have the misconception that being a man or a woman means having a set of stereotypical hobbies and personality traits. When a trans woman wants to be an engineer (insert male dominated field here) it's because she is really a man, but when a cis woman wants to be it's because she is determined and strong.
There are plenty of reasons that trans women conform to some stereotypes. Many related to safety. When you don't stand out you are less of a target, which is another set of issues that can be looked at. Others might just want to blend in and be "normal", for lack of a better word. Others are doing what every other person is, being themselves. This applies to cis and trans people but the harassment seems to be mostly geared towards trans people first.
Part of this is a hypercritical standard for trans women. The other part, I think, is people trying, usually intentionally, to maintain the status quo instead of embrace change. Cis women and men are criticized for not following gender norms as well but many times are celebrated for it. For example, a woman rejecting all makeup and the double standard set on women may be encouraged and praised for bucking the norm. A man just being a father that takes on all parental responsibilities, in the event of tragedy or otherwise, is seen as extra-ordinary instead of being something that should be rather normal and expected. There are instances where that same woman who bucked makeup trends would be criticized for not following the norm, say shaving her head or not shaving her body hair. Just because some inconsistencies exist doesn't mean they should be the norm. How can a trans person be expected to keep up with conflicting ideals? Trans women are almost universally criticized no matter how conforming they are or are not. The harassment of trans people leads to no good solutions. They would rather you didn't exist than have to introspect and realize what kind of person they are being.
People don't seem to deal well with certain kinds of gender non-conformity as a whole. The bar is set impossibly high for trans people, perhaps to justify the hate and discrimination. It is interesting to note that non-conforming leads to the same insulting behavior across the board. The two examples off the top of my head are: men insulting each other by emasculation, women who aren't attractive enough being called men as an insult. Perhaps most baffling to me is when the aggressor is someone of the same class. Most commonly this is seen in the form of gatekeeping. "You aren't a real woman if you don't have kids/cook/do X'. The irony seems to be lost on most people.
If you don't understand with the context of trans and cis I can put it with a common analogy that many Americans repeat for poor and wealthy. "The poor are just lazy and wouldn't be poor if they just tried". The poor are expected to better their situation by a far higher margin than the non-poor. A child born in poverty is expected to be able to grow up and escape that poverty and become well off despite their circumstances. Maybe moving from poverty to middle class. The child born to wealthy parents is not expected to become a billionaire. The wealthy child just have to not lose any significant wealth and they will be looked up to. Rather than trying to recognize this inconsistency the same people would say the poor person just didn't try hard enough despite being at such a disadvantage. This is similar to how it feels to be trans in a cis world. Start significantly farther behind but be expected to excel to be far above average.