Name one guy who came in, who is a bigger name than Styles that got buried?
RVD was in ECW and he eventually got pushed, before he frack up his own fate by getting busted with marijiuan. Jeff was a midcard wrestler before TNA made him into a star, and WWE capitalize on that.
I don't know why you bring up being buried by Cena, no one is going to dethrone Cena, you just got to accept that.
This is a different era in the WWE, and your assumption of WWE pissing on other company talents is a bit over-exaggerated. Kharma was in line of a huge push, before she got pregnant and didn't tell anyone before she signed. So, she got released.