"College" isn't just about cost or even just about education. It's also about experience.

1. No university can compete with BYU on cost: advantage BYU
2. No university can compete with BYU in terms of being around LDS: advantage BYU

3. But if you want a top education, there are many other universities to consider.
4. If you want to be part of an alumni base with top contacts, there are many other universities to consider.
5. If you want to meet people other than Mormons (BYU is 98.5% LDS) and experience a place other than Utah, there are many other universities to consider.

So to say that other universities are not worth the additional cost is to focus on 1 and 2 and ignore 3, 4, and 5.