I'm going to simplify it considerably and just speak about the basics:
Against a backroll if someone was good they can dash deep enough and time a clean launcher guaranteed on you since there is a frame during the getup where you are completely vulnerable and the launcher will land cleanly on you. Usually, people will just do a move that can interact with the hitbox of the backroll that can float you into a juggle state and the move has a small enough recovery to maintain the juggle for a complete combo.
People at a competent level can react to the backroll and hence you rarely see it in high level play.
Then then there is a quick neutral getup which is extremely unlikely anyone can ever react to so people try doing a hard read to hit you in between the frames of you on the floor and the frame you reach a neutral state and can block. If you do get hit it's the same thing as the backroll and you are relaunched... but the window for getting hit is extremely small.
You can sideroll, this option will usually get you out of any situation where people are fishing for ways to relaunch you assuming you'd do a quick neutral getup. If someone knows you're going to sideroll they're going to do their most damaging sweep or low move on your. If you instead chose to do a quick get up you'd do it fast enough to recover, block, and punish. Unfortunately there are some characters like Steve that have extremely quick d/f+1's that can relaunch you from a quick getup and recover so fast that that they have enough time to advance and pressure you further had you done a sideroll.
There are also the low and mid attacks you can do from wakeup. But they are not like VF or DOA where they have 0 invincibility and you can be counterhit and launched for doing them had someone read you doing it. Also, they're unsafe so you can be punished too for it. On the flipside if they hit in certain situation the reward is pretty great.
I'm not counting around 6-7 other options since they are specific depending on the location and type of attack done on you to leave you grounded. And I'm also ignoring the various ways you could be grounded such as Feet Up Head away, Feet up Head towards, Feet down Head towards, etc. since each of those situations has it's own caveats as well.
It does seem like a lot but I love the level of control you have over your character and the plethora of options at your disposal. It's something I really enjoy about fighting games.
Anyways, Tekken 7 is changing things where if you backroll whatever situation you're in, you're pretty much OK. HUGE departure from all the mindgames that were previously at play.