There's no feasible way to fit 70 runners on the track in the 10k.
There is plenty of feasible way to fit 500 people on a marathon start line. Maybe 2:25 isn't the number, maybe 500 isn't the number, but expanding the marathon trails and making it slightly more lax (also, since they charge a registration fee, all that does is boost the prize money - theoretically)
In that case, why not make it 2:35, or 3:35, or even 4:35. Charge $150 each. Think of the prize money!!!