How can glasses from Internet vendors be so cheap? How about quality?

as long as zenni keeps sponsors my newer favorite youtube music guy I’m happy with them Found the" professor of rock" channel on youtube anyone else watch him? - #2 by What_Exit

Since im on a state/federal medical plan I dont get to pick who does my glasses but last time I got glasses i expected to get the cheaply made entirley of plastic “medi-cal” specials that i always had…It was amazing when the guy who would be making my glasses and frames said ok the glasses are 795$ the lenses were 495 so i had 300 to use for a frame … I was shocked and spent 2 hours looking over designer frames like a teenager looking for a prom dress …the ones i picked out was 312 but the shop covered the 12 over

They lasted 3 years until i flung them at someone i was in an altercation … (it was that or a rock …)