Nobody is building big companies to prevent the world to crumble. They are build because it's possible for their owner, because their market is big enough, because of money, and because of the fun building them.

If there were only lifestyle business, investors would simply change the way they invest. They'll begin seeking lifestyle business that could explode with extra investment. Entreprenors would be probably get better terms as they'd be in a better position to negociate, but there would still be big companies.