Theoretical "perfect" competition eats all money that could go toward R&D, by making profits razor-thin. It's an awful way to exist that no sane person who's thought it through actually wants—assuming it could ever exist stably for any length of time, which, probably not.

Going the other direction, monopolies leave the most money available for R&D. Japan famously leveraged the power of a small set of huge players—not monopolies, but very, very far from "perfect competition" markets, certainly—to drive post-WWII R&D, ensuring their continued success by delivering them a captive domestic market while pooling their excess funds with cooperation-encouraging incentives (=more money, from the government) to rapidly improve their tech and productive capabilities, aiming to become an export powerhouse. It worked.

This is not meant to be a defense of monopolies, especially those not firmly under the yoke of government to ensure all that excess is captured in some way for something resembling the public good, but the situation is more complex than one might first think, and whether one may prefer a huge number of market participants or a small number could be very much situational.

They can avoid unnecessary redundant infrastructure as an example. Imagine trying to dig for construction when there are 30 potential cable companies running utilities underground.