Probably just because of how large the airfield is. This MiG-29 is very close to the dimensions of the real one (for example, being 17 and a half metres long), with maybe a 1-3% margin of error. The Yak got downsized to be more in line with its real-life counterpart a while back so it's reasonable for this to be as well - and it is still a fair bit larger than the Yak.
Bear in mind that the airfield needs this much room to allow plenty of leeway for taxiing planes to pass each other with minimal risk of lagging into one another and either wasting time or one getting pushed off the runway to their death.
Pushwall
Robert joined
Lead Developer of Red Alert: A Path Beyond