There was a whole variety of different cases brought by different groups in different states over different issues. The rulings are all online - you can look them up if you want. The Trump campaign actually did win some cases, though most of these were before the election, which is when most election litigation usually happens. Generally the post-election losses came down to one of the following factors:

• the plaintiffs were not directly involved in the dispute (i.e. they weren't candidates or campaigns) so they didn't have standing

• they were trying to fight state law issues in federal courts

• they were trying to relitigate stuff that had already been dealt with by previous cases

• they were trying to dispute long-established election procedures just before the election or after the election

• the small number of cases that were actually focused on fraud only offered really flimsy evidence, including a lot of hearsay ("our witness says that somebody else said that...") which is generally not admissible, and expert witnesses who clearly had no idea what they were talking about (e.g. one was an anonymous person who claimed to have worked on missile systems and argued that this made them an expert on voting machines)

Tbh I suspect that most of the people who brought these cases knew they had no chance of winning, and were just doing it for the publicity or whatever.