IP laws are a negligible factor in the dominance of tech giants. When was the last time Google or Facebook sued a startup for violating one of its patents? It's far easier to just buy them out.
These companies have absurd amounts of proprietary information on everything going on in the world, and it's near impossible to compete. You are right, they will generally just buy you out, but if you don't accept, they will buy out your competitor and then your competitor will suddenly have access to all your customers (and many more), your potential customers, your usage numbers, data on your employees, your financings, et cetera.
It's not a fair fight, and it is the way it is because of ImaginaryProperty laws.
