Problem being that community colleges will happily lie to your face about what does and does not transfer and most community college students aren't going to lawyer up about it.
That's more on the universities end than the CC, I used to see it all the time. The community colleges would have agreements with many universities but when you'd as the uni to accept your credits they wouldn't and you'd spend 6 months fighting it. I took a calculus class at Purdue over the summer and tried to transfer it to Indiana and they flatly rejected it -same state, same class, won't accept it. Everybody has their little fiefdom and they will fight to the death to keep it.
By denying course transfers Universities benefit. Students are forced to enroll for additional quarters. The university could make tens of thousands of dollars per student on a few course transfer denials.
This comes at an enormous time and money cost to the student.
A good alternative would be to test proficiency for that class. But that’s additional work a University has little desire to do, beyond allowing for testing out of precalculus.
To be fair, what transfers is determined by the school you're transferring to. Then on top of that you have to match up the requirements for your major, i.e. you might have a CC science course that is accepted by the university but doesn't meet the science required by your major. I suspect there are a LOT of CC students who only have vague goals of transferring somewhere to finish a four year degree (I was one of them many years ago), and in many cases it's just going to be difficult to give them solid advice.
The program I successfully completed had detailed written documentation from both the CC and uni at sign up time, of exactly what needed to happen as part of the organized official admissions program. Grades had to be above C IIRC and they were very specific about exactly which "electives" we were permitted to select, such that they were not really "electives" they were just non-major required courses if you wanted to transfer in with 64 credits. IIRC I willfully took some different electives and ended up with only 48 or 56 credits but I had written documentation explaining what I did.
I do believe there is airy and non-specific marketing material about "take your calculus class at CC and transfer to some schools" in a non-specific manner that is, as you claim, sort of fictional. Or "many of our classes transfer to state-U" which in a legal sense is technically true.
It isn't likely that they are intentionally lying. What is and is not accepted is dependent on the school and the other school can change their mind at any point and the community college has no control over that.
I did this and was 100% successful, although the article propagandizes by asking what percentage of students once considered possibly obtaining a bachelors degree in the future which I'm sure is very high, whereas I was in a specific program with a specific track directly primarily toward cooperating with the transfer schools, so our success rate was very high (something like 80% got their BS degree along with me).
Also my CC fed the state U system and three private colleges, not solely state U.