I don't think prostitute was "always" considered offensive. Before the 1970s the words whore and hooker were replaced more and more by prostitute, to be more polite. The term sex worker is pretty modern. The use of escort for sex worker (and not just someone to bring to a corporate event or wedding) is also seen more often.
I take your point, however, 'prostitute' was never polite and was used in the UK much earlier than the 1970s, apparently used here since the 1500s here. It has only been very recently replaced with sex worker which gives the recognition that people in sex work are actual workers. Which they are
The use of prostitute is very common in scholarly circles. In fact, when the Hebrew Bible is translated into English, the Hebrew word "holy ones," qudesha, used to denote the sacred representatives of various goddesses, who blessed men by having sex with them in the temples devoted to Asherah, Astarte, Inanna, etc., is to this day, (grossly) translated as "temple prostitutes," instead of as the literal translation of "holy ones." It makes me ill. Worse, the word for male temple sex workers, qudeshim, is translated sometimes as "dogs."
"Escort" was the one they used in the classified ads because "sex work" was (and still is) illegal here in Butt Hurt, OW. Nowadays with the internet, "escort" has given way to "adult companion" and similar expressions.
The word trollop is by far my favorite. The way it bounces around the tongue and smacks the lips is so in line with the meaning of the word.
