The benefits of m43?

I've been looking for a new camera for a while. Owned a lot of cameras before from Nikon, Canon and Fuji (but Fuji was a P&S).

I can't just grasp how Pana and Oly can charge as much as they do for their cameras. I am just thinking of plain economics, when a competitors offer looks better than the other consumers usually goes for that. And Sony can offer a full frame A7 with a good kit lens for the same price as a top-of-the-line m43 with a decent lens.

And that is my question. As a hobby photographer with high ambitions, why should I choose to go with m43 when everything points me in the direction of a full frame, which is the 35mm format that I am used to? The only thing that I can think of is size, but the difference is only in a few grams and not kilos.

Hopefully Pana and Oly will lower the price of their offering to compete with what Sony has put on the table. Because I can see myself wanting one of their longer lenses and lesser cameras to do birding. But I think lower prices might be the only way for them to stick around in the long run.

Or what do you think?

BR
Celso Abadello