Novena's a pretty amazing project, but it's not nearly as polished as this purism laptop appears to be. It's (intentionally) a hacker friendly box with lots of space and less integration than a normal laptop. It even uses a RC hobbyist style battery. Novena is a labour of love driven by a particularly skilled person.
To design and mass produce a laptop as slim and well integrated as the Purism laptop is significantly more work. To do so having never produced a laptop before would cost even more so. $250,000 really is a small amount of money when you're trying to mass produce cutting edge consumer electronics.
Of course they may (almost certainly do) have other sources of investment.
Novena[1] had a total budget of ~750k$. It was done from scratch, with some nonstandard (and somewhat expensive) components (e.g. an fpga; it had a software defined radio included too, though it was a mostly-off-the-shelf-one).
[1] https://www.crowdsupply.com/sutajio-kosagi/novena