Anything after the Rocket Science tech for probes is considered optional. The most expensive tech needed to win the game and get the victory screen is 100k. These optional techs mainly give you stuff like personal equipment that doesn't really require you to redesign your whole base around them. Think of them as filling the same role as vanilla infinite research. Vanilla infinite research can scale up to hundreds of millions of research if you keep playing long enough.
Optional goals like these give people who want to build a megabase something to actually use their megabase for. In addition to the traditional infinite research, Nullius adds some more tangible alternatives to make it a little more interesting. People who don't want to scale up to a megabase are free to check out at any time. If you complete the mission goals, you're considered to have finished a Nullius playthrough, whether you unlock the final few optional techs or not.
For people who do want to build an end game megabase, Nullius offers some interesting late game options. All the biotech you get in the end game can replace some of the big bottlenecks holding back your SPM. So you can scale up using the new and cheaper biology recipes and scale to a higher SPM more easily using the new tech. This stuff comes so late that if you're only going for the victory conditions, it's probably not worth bothering to incorporate them. But having a more ambitious goal beyond that gives you a reason that you might consider actually making use of those end game recipes. For people who would rather call it done than go for a megabase, they aren't forced to do it to beat the mod.
