Have you not been reading the papers? ICE is currently looking for 300,000 aliens that did not show up for their deportation hearings. Many of those are felons. That’s why ICE and DHS have made them a priority.
The only time they get deported is if ICE knows they are in jail and informs the jail to tell ICE when they are to be released, so ICE can pick them up. There is currently no tracking system for illegal aliens in Local and State jails and prisons. It’s all hit or miss.
As I suspect you know, local and State jails don’t coordinate with ICE very well and ICE does not coordinate with anyone very well.
I'd bet a lot of these illegal aliens who commit felonies have their sentences plea bargained down to a misdemeanor by liberal judges. Isn't that what happened in New York City a couple of years ago when that gang of illegals kidnapped and raped a woman. A couple of those illegals had run afoul of the law before but of course NYC has some kind of sanctuary policy involving illegal aliens.