A one-off 300K isn't a lot for two people to live on if it would cut off their donation stream completely, and if you've been doing this for 10 years it may not be easy to find a job.
There are still a lot of employers who see time spent on your own venture as a gap in employment history. I mean, I guess it literally is, since you aren't an "employee". But they completely discount any applicable experience during that time.
The founder Tarn Adams has a Ph.D. in Mathematics from Stanford, so I don't think any of his potential employers will mind that he spent his time working on a fantasy economic simulator of this scope.
I think it's indicative of the value of the property that just the name alone is worth 300K. If they were interested in commercializing the game I suspect they would be able to make a lot more.