
As others have said; originally, the covers did what covers do; cover stuff up. Sometimes "unsightly" stuff - like that bent plate bridge; you have to admit that, as good and functional as it was (and still is), it'll never win a beauty contest. And, until... the late '70s?... Fender basses wore flat wound strings from the factory. And you don't have to change flats every time you turn around, so who cared if it was in the way...

Sometimes, covers protect "delicate"/"sensitive" stuff. Like pickups; which, back in the day, could be sensitive to RF nonsense. As for interfering with your playing? Watch videos of bass players back when these basses were a new thing. Hardly any of them played all over the strings; you didn't need to, when bass lines were "thumpty thumpity thump - change up - thumpty thumpity thunp - change down..." Just use the thumb rest - or the tug bar - and play... If you play like that? The covers aren't a problem at all. What the "problem" really is, is that music changed, and playing styles changed with it. Tug bars, thumb rests, and covers (with a mute) did become an impediment to playing, and people just yanked that stuff off. Fender finally wised up, and didn't put that stuff on their basses any more.
My '78 P-Bass still had all that stuff on it when it was new; the original owner took them off, like everyone did at the time. When I bought it from him in 1988, I put it all back on - including flats
and the mute in the bridge cover. Why? Because the music I like to play was played with a P-Bass set up the original way; I play in front of the pickup cover with a pick; and, mostly, the bass lines for the music I play, are "thumpty thumpity thump - change up..." It brings back memories of good times; the band I was in and the music we played. It makes me happy; and I don't have to please anybody but myself...
