Why don't protostars mature?

Question

Why don't protostars mature?

Answer 1

Same reason children don't mature - in other words, of course they do, and possibly more predictably. We just happen to be seeing them at that point in their development. With lifetimes in the billions of years, stars live much too long for us to be able to watch one grow up. Only rarely do we get to observe a star in transition, and often we can't tell for sure which transition it is.

Answer 2

They do, but only over a timescale we cannot truly appreciate.