What's up with this guy in the 80's?

Retarded take and i'm nor evwn a zappa or miles fan. You are basically a rockiat but in reverse

he had his home studio that just didn't sound as good as the commercial studios he'd used before. compare the sound of an album like them or us/drowning witch to Joe's Garage and you'll see.
In terms of musical direction it's when he began to fragment. His stuff in the 80s still has a lot of interesting material, but there's a lot of songs like he's so gay, in france or be in my video where he's clearly writing to formula, down to the chord changes and structures being super predictable and the same as several other songs of his, and it's just not that interesting. And his more interesting material from this period like drowning witch or sinister footwear is much more dense and less accessible than something like Inca roads. Whereas before the 80s his material was an unpredictable mix of stuff, as the 80s went on it was a more regimented split of goofy doo-wop/blues filler, dense modernist pieces arranged for his touring band, and long guitar solos removed from their song context.

Joe's Garage was the first album he recorded in his home studio after his label fired him
The entire album is a metaphor for being fired by his label and worrying about losing his musical career

Why does he have to wear blackface then?
Was it to portray his musical slavery to the label?

The pic was several years old, it was an unused shot from a prior album cover shoot he had saved
He was broke when he finished Joe's Garage, basically put every cent he had into recording it and probably used the old shot because grease=mechanic=garage is close enough and since it was free it was basically what he could afford
You have to remember Zappa had just been fired by his label for consistently losing them money, had never had a commercially successful album, and spent his life savings on Joe's Garage

Did he spend too much label money on researching catholic girl's behaviors?

I had sex with him

Did he buy you a pizza?

Zappa always did pretty well with synths. Whether or not you like his Synclavier output (I think at least Jazz from Hell and Civilization Phaze III are good), it let him do what he always wanted to do. So you're totally wrong on that.

his mustache is made of carpet trimmings.

Solo Zappa was complete shit. Only The Mothers of Invention were good.

What album was made with synths?

uh lots of them
youtube.com/watch?v=YgRSNSqpJeo
he used analog synths a lot in the 70s too