They adopted that haircut because they thought it would help them better interact with humans. They intercepted a lot of television broadcasts and decided this was humanity's greatest champion.
The vulcan science directorate has determined that there once were two hairstyles in the past (the second probably having something to do with Romulans). They also determined that time travel is impossible, hence just one hairstyle now.
Original series T'pring's attitude could make any hairdo look good. You gotta believe in yourself as a triflin', intriguin', spicy murder senorita before you can pull it off.
Shouldn't they simply all have a buzz cut? Easy to maintain, easy to keep clean even in difficult circumstances, never gets in the way. Just the most logical haircut.
I'd be remiss if I didn't point out that you have two pairs of the same person and that more than half of these examples (Solkar, Spock, Sarek) are sourced from a single family.