Many trains don't seem to have them these days; and I suspect one or indeed both of the following reasons:
1: trains are so grotesquely overcrowded on many routes, the inspector can't physically get through the train, or;
2: they get so much grief from passengers that they daren't go into the cars - telling people who've spent £x thousand on a season ticket that they shouldn't stand in an exit, or telling others that they should find somewhere to put their luggage other than the tables or aisles when there is no luggage space* - can't do much for morale.
* no, I have to say it - don't stop me now. What TWAT developed the interior layout of Virgin Pendolinos and put luggage racks in the middle of the cars? Meaning you have to walk half the length of the car down a narrow aisle to stow your luggage, THEN turn around to fight your way through the rest of the crowd trying to do the same???