AT&T was a large tech monopoly during much of the 20th century, controlling most of the communication market in the U.S. and Canada. The ability to set prices allowed AT&T to fund long-term research and development for some highly-regarded innovations, such as the transistor. Without the ability to set prices, AT&T would not have had the necessary capital to fund long-term projects like the transistor. The transistor took more than 15 years before it began to develop into what it is today: hardware used in nearly every digital computer. A smaller tech company without a monopoly would not be able to invest the resources needed for long-term innovations like this because the effect it would have on their bottom line would not be sustainable. Further, these long-term innovations foster others: the transistor developed in the 1940's gave rise to the microchip developed in the 1960's.
This is assuming that the company relies solely on its monopoly for profit. If a company is large enough, it may have the ability to diversify its assets without innovation.
[P1] Monopolies will use the profit that they obtain through price-setting to fund research and development, because if they don't another company may create something that makes their entire monopoly obsolete.
Rejecting the premises
[Rejecting P1] Though they may use some of the profit for innovation, the immense amount of capital at their disposal allows them to simply buy out competitors when they begin to appear.