I have been wondering why ST hindered careers of many cast members. Has it been a common phenomenon, that a star in a TV series tends not to be able to land another starring role after the show is cancelled?
Most definitely. It's called typecasting. In the 60s, actors were signed to contracts that stipulated they would get royalties for two repeats. Since, in the 50s, many shows went out live, the concept of
any show getting
two repeats in syndication seemed unlikely but quite generous. So the casts of popular shows like "Batman", "Gilligan's Island", "Lost in Space", "Star Trek", etc., got quite a shock a decade later when they
received no more royalties, and were still being seen/overexposed every day - and yet their colleagues were signing onto shows in the 70s and 80s, which had new clauses granting them royalties for
every repeat.
An example: an actor friend of mine gets cast in "mother roles". A prime time show she did for two years went into afternoon repeats about a decade later and suddenly all her acting work dried up. She asked her agent and was told that the repeats were overexposing her. Casting directors were turning her down (before audition) because she was considered to be "in work". But her royalty payment was too small to put food on her table every week. After the two years of repeats finished, she started getting offers again.
Remember that some of the supporting cast of "Star Trek" represented
minority groups. Hard enough to win auditions in the caucasian Hollywood of the 60s and 70s, let alone when you're being seen in repeats
every day.
Most people don't get any opportunity to publicly complain about it (unless it's harassment or something more serious), let alone complaining about it for 45 years.
And the cast themselves did not do much "complaining" until the early 90s. Publishers like controversy to sell books.
When the cast all started writing their autobiographies in the early 1990s, we suddenly heard about Takei and Doohan describing Shatner's scene stealing, and Grace Lee Whitney's problems with diet pills, alcohol and sexual assault, and Nichelle's formalization/elaboration of her Martin Luthor King story. The media keeps repeating the stories, and they grow and grow.
None of them have been "complaining about it for 45 years". As I said, the convention appearances are delivered quite tongue in cheek - the ones I've witnessed anyway.