So what you seem to be suggesting is he should spend his entire net worth all in one go right now and then walk away, and if he doesn't he's a fraud? If that's what you mean, it doesn't seem to me to be a very effective strategy when tackling long term problems, especially as new problems keep coming up. No investments means no revenue to tackle new problems.
Do you really think committing everything up front would be a better use of his resources?
They do support some GMO research as part of their commitment to improved agricultural output and food security in the developing world. I suppose it's a case of conflicting priorities. They've been into reducing poverty and hunger longer than they've been into environmentalism.
Even then it's not a straight trade-off. GMO can have harmful consequences, but if it reduces the agricultural footprint that's an environmental benefit.
Do you really think committing everything up front would be a better use of his resources?