Welcome to FT!,
Steve from CA
Unfortunate set of circumstances, Guess the question is what did you want UA to do?
The 14 hour / overnight not able to check-thru bags is a clear UA policy and is on the website, guess UA could have waived that policy. How is their policy "wrong?" It is inconvenient but it is what it is. ANd it would have not changed the outcome.
The fact of a 14-hour layover violated the Costa Rican requirement of a max of 12 hours, UA could not waiver that and could have been fine many $$$$ if it had.
The 14-hour layover did mean you had a break in your flight and your USA departure was Houston -- for future reference, there are more frequent flights to Houston from San Francisco and it may be a better use of your time to use SFO vs SMF ( Sacramento ) for these trips. A longer drive, but shorter connection at Houston.
UA could not help you find a hotel as the Costa Rican requirements do not allow you to leave the airport (unclear if the Houston Marriott was an allowed choice)
The fact the US State Department site was inaccurate was not UA's fault nor is it the rules UA most follow.
It is unfortunate you did not feel well treated but these entry requirements are complex, confusing, and do not provide any leeway by UA.
On the surface, it looked like this trip was "broken" from the beginning and it is not the airline's responsibility to validate your trip choices at booking as the number of options are vast. It is UA's responsibility to check on day of travel if you meet the entry requirements UA finds on "IATA Timatic" -- the industry's authoritative source of entry requirements (which the US State Dept is not). UA provides passengers access to
TItmac on the United site. It is referenced in your online reservation.
Travel in today's COVID entry restricted world is a mess and unfortunately, you and others have gotten caught up in it.