TDoR was established because trans people who are murdered are often deadnamed, or not named at all, disowned and denied by family, treated as refuse by police and other officials, and quickly entirely forgotten. (The lists usually include a lot of "name unknown"s.) If they're lucky and were part of a trans community (always pretty small and usually outcast), their friends might remember them for a while, or even light candles near where they died. Society at large tries to forget they ever existed. This is still a problem even now, over 20 years since TDoR was established. TDoR is a way of making sure that they (well, the ones that we know about) aren't forgotten.

We do TDoR ceremonies for the same reason cis people do funerals and memorial services. As for "showy," most funerals are more showy than any of the TDoR ceremonies I've seen. In my experience, TDoR ceremonies usually consist of a few people speaking (I read the "no man is an island" passage), maybe a few people playing music, and a reading of the names. Often, only the USA names are read, because there are so many international ones. They don't seem to have a high profile; I never hear about them in the news, except maybe the LGBT news sites, and I usually have to ask around and do a bunch of web searches to even find a local ceremony.

I also see it as a form of resistance: we're saying, "we're still here, we won't be eradicated," even if we're the only ones who hear it. If you and your friends don't have to worry about being murdered or hounded to death, nor that you or your friends will be quickly forgotten by all when you die, you are fortunate. (Well, I guess I am, too.)