Yep, these were explicitly designed this way. Basically, here's what is going on:
1. First guys into space just kind of barely squeak out into space, because hey -- they're the first since the Hydrals. Plus you jacked their flagship.
2. Second guys into space are right on the heels of the first, because they were in a desperate run to steal all the first race's stuff and duplicate their work as quickly as possible.
3. Third and fourth guys into space were also stealing as fast as possible, but they know they are a bit more behind. So before they actually launch, they take a tad more time and launch more ships at a go. It costs them time in space, but it does make up a bit for them being late.
4. Fifth and sixth guys into space know they are really not winning this race at all. Right now their only real recourse is to hope nobody notices them much at the moment while they build up their fleet in semi-secret. It's going to take them way longer to do that than it did the earlier races, you'll notice. But when they do burst onto the scene, they have substantially more stuff kitting out their launch fleet. They might even catch one of the earlier races at a time of weakness if they time it right! They've also had the benefit of spying on the other races actually flying around and doing stuff, so they've had all this extra telemetry to use to refine their work.
5. Seventh and eighth races know they are in an even worse place, but their strategy is much the same -- just taking even longer to pull off. They could either launch early and get obliterated, or they can wait and study and launch with a larger force. Really the only way to survive, so they all wind up making that their choice (actually it's coded into the design of the game, but there's no other viable strategic decision in my opinion).
Hope that makes sense in terms of what the lore reasoning is here.
Cheers!
