What is huge? One gold album and disappearing for 6 years until Big Pimpin? Teach me about huge, Juvenile was huge, No Limit were huge, Outkast were huge, Scarface and on. UGK? I don't know.
I don't know when everyone started fukking with Jay in a region of like 150 million people that spans from just south of NY to just east of Cali. I'll assume that it didn't happen overnight, my assumption is that those two joints from 98 introduced him to hiphop stations in the south and made people buy his album. That took place in the same time as Jay sold 5-6 million copies and was all over MTV too. The year after he has sold out tours in multiple southern cities.
UGK didn't disappear until "Big Pimpin". They were on huge albums before "Big Pimpin" ever came out. Pimp C was on Master P's "I Miss My Homies", which was a single, from his biggest album Ghetto D. They were also featured on "Break Em Off Something", which came out in '96. They were on several albums from No Limit and Cash Money, and several compilations and soundtracks before "Big Pimpin". Before this, "Pocket Full of Stones" is the song that put them on the map.