I think I have good reasons so don't kill me just yet.
My reason comes down to the fact that something so good (the armor) had such a terrible introduction, and by this I mean game breaking, as a result it carries one of the most bitter experiences I have of Fallout 4.
(There is a video which covers my reasoning: https://www.youtube.com/watch?v=aoIusEhRPRs)
Most players know you can find and wear a full set of some of the games best power armor within 20 minutes of starting Fallout 4. The reason this is such a mistake is fairly clear. The purpose of RPGs like Fallout are to start you with a weak character with very few abilities, you then can craft and upgrade your character the more you play the game.
It Is disappointing because arguably one of the biggest gameplay alteration and improvement in the game is effectively given to you with no effort of your own. You haven’t earnt this achievement past the effort of earning the money to buy the game. It sours your later achievements because you have already pretty much reached the top, and other achievements are a lot less significant in comparison. It is important to note that the usefulness of your Power armour is reduced because it requires fusion cores, but these are not hugely rare and do not change the fact that the power armour can be used so early on.
Considering all the negativity I have around this, I will explain how this could be improved rather than just give mindless criticism. First you could have seen someone in power armour early on in the game. Like someone flying past with it, or NPCs using it and showing how good it really is. Or to be even more sure the player gets this experience perhaps Shaun could have been taken by a character in power armour smashing open the stasis chambers in the vault. This ensures the player feels a connection with power armour and actually see why they want to acquire it.
Secondly the power armour could have been given to the player in stages or increments, that build towards you being able to use it. Each time you find a new suit of power armour somewhere in the wasteland it should be so broken you cannot enter it because the skeleton holding the armour is not working. You can still savage the pieces attached, like the helmet and legs, but the skeleton is too damaged to work. The player can however salvage a working piece from each skeleton they find. The player would need to find a full set of working skeleton pieces, which they could then join together to make a full working skeleton that can be used. Until you have a full skeleton the power armour cannot be used. This way you are continuously working towards getting a full set of working power armour. It would add anticipation for the player and a longing to acquire this final suit of armour which requires time and effort to achieve a reward.