One reason the idea of eliminating COVID was nonsensical is that it's carried by many animals, like all coronaviruses, and can be transmitted from humans to animals and vice versa. Measles, by contrast, is thought to be human only. So anytime there is an outbreak it's not from an unknowable cause. It's going to be either from a foreigner or somebody who visited a foreign country and returned with the virus.
Various social decisions have led to countries you might think of as measles free, no longer being measles free. For instance Canada, the UK, Spain, and obviously Mexico are all now considered to have endemic measles, with Canada and Mexico already compromising the majority of visitors and "visitors" to the US. And the vaccines are not complete immunization. Double dose measles is around 97% effective, meaning you can expect at least 3% breakthrough infections, possibly more depending on factors such as age, immuno compromisation, degree of exposure, and so on.
Various social decisions have led to countries you might think of as measles free, no longer being measles free. For instance Canada, the UK, Spain, and obviously Mexico are all now considered to have endemic measles, with Canada and Mexico already compromising the majority of visitors and "visitors" to the US. And the vaccines are not complete immunization. Double dose measles is around 97% effective, meaning you can expect at least 3% breakthrough infections, possibly more depending on factors such as age, immuno compromisation, degree of exposure, and so on.