Of course it is excusable for flight crew not to talk to the passengers although it is not ideal! It depends on the length of the sector.
Company policy is always to do a PA. Flying is all about priorities and sometimes PAs are near the bottom of the list, sorry. There are times when it just isn't practical to do a PA for example when trying to meet a very tight air traffic control restriction before departure, or when given a last minute runway change before the top of descent, the aircraft has to be set up for the new approach and the approach rebriefed (note the CAA frown upon PAs during the descent).
ACARs, I am sure there was a very good reason you did not hear a PA.