IMHO people think synths sound corny because the corny pop from the 80s is the first time synthesizers were embraced and had to be explained in white American popular music.

Stadium rock and pop took influence from the European pop that wasn't afraid to use synths. Remember, the same cultural forces that begat punk also "killed" disco. Electronic music in America was verboten for a while for white dudes, lest you be considered a nerd or gay. Europe didn't have those same hang ups and imported and internalized the synth music the white guys with guitars didn't listen to.

This also coincides with cheaper, more stable, and more playable synths being introduced. It's easier to tour with something you can save presets on. And a saw tooth cuts. That's important when you're playing a stadium.

So, you turn on top 40 and hear that Van Halen sawtooth for the first time, or see some weirdo playing a keyboard like a guitar, or whatever, it demands an explanation. The sounds are so novel to the style and so out of place they stand out. Novelty demands definition.

It's sort of ironic that the first time American Music Media stopped regarding synthesizers as novelties was with genres that used them more or less as novelties. But there's a long history of whitewashing electronic music. I don't want to rant. I'll stop there.

It also has to do with how tactility is embedded in our operating definition of what an instrument is. I go to the music store and strum a guitar it sounds like a guitar. I plink some keys of whatever floor model synth and it sounds like a corny preset.