I believe on the ATP/Challenger circuit it's pretty open, after all, there are the press offices, you can submit articles and tweets as early as you want (despite tournaments also having official livescores and betting companies scoring and streaming). For some reason, at ITF tournaments it seems to be a problem though.
Only exceptions are tournaments where gambling companies are main sponsors, in Kitzbuehel (and Hamburg, I think) credited journalists are forced to sign under rules they will not tweet from the things that happen in the match (even if a squirrel shows up on court). To be honest, I don't like this rule at these 2 tournaments, but maybe I'm biased due to being a journalist myself, maybe other people think it's fair enough if the gambling company gives money for the tournament to happen and they have exclusive rights for this. I don't know.
Understand your post but it doesn't explain WHY they don't want you doing it? Unless I am missing something?