Because to hire/pay a competent programmer can be anywhere from $60-90K/year and that's if they're just starting out. An artist who's just landing his first gig in the industry at a studio will likely be paid $40-50K if they're on a salary. I can't speak for designers, but I would assume they get paid as much as artists at the very least.
I'm going to go ahead and assume that he's not going to be using newbies for this game but whatever, I'll use the high end of my estimates. Salaries alone for a 6 month dev cycle with an assumed team of 10 people will come to at least:
- 5 artists: $25K each for a total of $125,000
- 5 programmers: $45K each for a total of $225,000
That's a total of $350,000 and I'm assuming that he's using new entries into the industry, isn't paying any overtime, no contract work, etc., etc. $400,000 is a really, really low budget.
And that's before they pay rent and utilities on the premises, any contractor fees and before Tim himself draws a salary.
It's awesome that you think about "these kind of things" but come on! At least try to think a little harder . . .