My (limited) understanding is that Romania were very strong for a number of years, but slowly started dropping off, partly due to coaches/trainers defecting to USA and other countries, partly due to the sport having a bad reputation for abuse and cruelty so parents didn't want to send their kids, and partly due to lack of investment in the sport. They hung on and by the early-mid 2000s with just enough talent, but very little depth - if anyone got injured the team would be screwed. In more recent years they haven't even been qualifying teams to team final (top 8 teams in the world). They typically always have at least one great gymnast, but not the powerhouse country they once were.
They have a beautiful all arounder, Larisa Iordache, who qualified to be in Tokyo, but very sadly she hurt her ankle in qualifying so will only appear in the beam final.