The issue is not merely finding actual instrument flight conditions. One must find instrument flight conditions that are safe to fly in. One must avoid icing, excessive wind, excessive turbulence, thunderstorms, mountain wave, widespread below-minimums weather, etc., etc. The farther you have to go, the greater the chance of encountering unsafe conditions either along the way, or at the destination. And there is also the very real possibility that the IMC you are chasing may evaporate before you get there. I can't count the number of times I have taken off looking to renew my instrument currency in IMC in the Monterey Bay area, for example, only to have the weather improve enough to defeat my plans, and that's only 50 miles away.
Furthermore, the farther you go, the greater the chances that you will have to pay for overnight accommodations for yourself and your instructor, and there's no guarantee that the weather will be safe to fly home in the next day. Meanwhile, you're having to pay your instructor not only for your lesson time, but also enough to compensate for his or her lost revenue from not being able to schedule lessons with other students while away from home.
It's just not as simple as some are making it out to be.