Presumably you are (somewhat) conflating large companies in general with monopolies. This needn't be the case. For an example, see some of the world's duopolies, such as in computer hardware (think amd + intel or amd+nvidia) in these fields, despite there being a leader, the presence of another often causes impetus that leads to research.
See IBM, google etc.
Otherwise it's disrupt or scrape along the edge of profitability at a race to the bottom, no?
(I'm not claiming to be right, it's a complex thing I don't know enough about for such claim)