2 questions:
1) Why not?
2) So what?
1) I wasn't making a judgement in this particular post, so your "Why not?" seems to me to be an attempt at some sort of childish sophism.
2) So adding most popular subclasses doesn't necessarily lead to increased build variety.
Is there some force that forbid you building an abjuratuon frontline wizard and makes you pick bladesinger instead? People can do what they want. More options is always better
Just pointing out that more options don't lead to actual increased build variety. Building character to some extent will always have to consider it's comparative power to other options. At every step of building a character you make a judgment based on what works better.