I hate to be that guy, but this needs to be said. The guy on page 15 was right. Sage
should have at least put a little more effort into their applications, because if it did, it would be much more popular and thus more developed.
Back in 2011 or so, as a young undergrad, I latched onto sage and used it for an undergrad research project. My BS was from a tiny university (one year, I was the only Physics major in the school)..and I tried to turn all my friends and profs onto sage, being small meant there was no dept. standard, so I tried to impress it on the dept. (3 people really) but they stuck with mathematica because sage didn't even have an easy to use ode solver! For pete's sake... I understand that sage is a niche project for the math community, but if that's the case, that's the only place you'll find funding and devs from.
This is often said here amongst the startup nerds: make sure you have an audience willing to pay. Hey, many of us in the "more applied community" would love to have a FOSS tool that rivals mathematica, we exist! But it needs to do things well, or at least well enough that in linear combination with the fact that it is open source, the overall goodness vector for the project's value has a timelike norm. Then, we'd clamor for it, you get downloads, and one day, the funders will go, "hey, that's good shit right there, I better be a part of it!"
They don't need to do things for others, or for others' interest. But then, no one should be surprised when such efforts don't get funding. I mean, doing something niche implies that less people will be interested which implies that less people will fund it, right? It's almost a direct consequence of choosing to serve a niche.