It's considered standard practice to always crouch-block by default - highs are traditionally slower than lows, so crouch-blocking blocks everything but "reactable" highs and you only need to look for and respond to one option.

It's also worth noting that not losing isn't the same as winning - that defense is only as good as the offense it enables. Someone with okay offense and zero defense will get more results than someone with okay defense and zero offense. That being said: punishes are offense and bad players LOVE to throw themselves at their opponent and self-destruct, so learning to block, punish, and anti-air gets you out of low ranks pretty quickly.

Blocking and defense in general is pretty knowledge-heavy and varies by the character you're fighting, so it's usually properly learned last after offense and neutral. Strong defense is highly respected and considered an exhibition of the player's skill (both in the genre and the specific game they're playing). So don't beat yourself up every time you get mixed.