What am I missing as a beginner to the instrument?
It's situational.
If there is a specific lick that has to use an open string, then fine, I'll use an open string. But only if there is absolutely no way around it. Like a pedaling lick.
For everything else I use closed positions. I play in a lot of cover bands, Soul, Motown, Classic Rock, Blues, Pop, Etc., and singers constantly change keys on me. If I learn a song in A and use lots of open strings, then get to the gig and they want to do the song in G, well that's a problem. But it's not a problem to change keys if I learned the song without any open licks. I can do it on the fly.
In my world of old farts there are two types of bands: Guitar bands, and horn bands. Song keys are all over the place based on the genre of music and the keys that a singer is comfortable with. If a horn song in F is being covered by a guitar driven band, there's a 99.9% chance the guitarist is gonna want to play it in E. And the singer will nod, happily.
So my reasons are more for efficiency. And for the record, I much prefer the sound of open bass strings.

Fretted strings are easier to control. Muting, damping, whatever you want to call it, is really important for me, so being able to control the beast that is the bass, and change keys on the fly are really the main reason I play almost every note fretted.