The Electoral College is fundamentally undemocratic—it allows candidates to lose the popular vote and still become president, as happened in 2000 and 2016. Every vote should count equally regardless of where you live, but right now a voter in Wyoming has roughly 3.6 times the influence per capita as a voter in California. A direct popular vote would make presidential campaigns actually compete nationwide instead of ignoring 30+ states as "safe."
The Electoral College forces candidates to build geographically diverse coalitions and ensures that small states and rural America aren't completely steamrolled by high-population urban centers. Without it, campaigns would only focus on a handful of densely populated metros, leaving huge swaths of the country politically irrelevant. The Founders designed it this way specifically to balance federal power—eliminating it would centralize power in ways that would fundamentally weaken the federal system.