The various trials and probes serve overlapping purposes:

- Definitely to drain his time and money and attention from campaigning
- To reduce his stature as a candidate and make him appear shadier
- To generate derogatory Trump content for the news cycle
- Possibly to create unhealthy mental stress in Trump so that he breaks or has a medical episode before the election.
- To convince normies that he really is terrible in all ways.
- Possibly to "win" his convictions but more important just to keep up a drumbeat of "Trump bad".
- Possibly in the event convictions are won, to leverage it/them to trigger legal prohibition against him being placed as president.

Your question suggests that there is more than the surface level points to this, and I honestly don't think there is. It's just Trump open season.