The electoral college is fundamentally undemocratic—it allows a candidate to win the presidency while losing the popular vote by millions, which happened twice in 20 years. Why should voters in Wyoming have exponentially more power per capita than voters in California? A direct popular vote is the only way to ensure every American's vote counts equally, regardless of where they live.
The electoral college forces candidates to build geographically diverse coalitions and prevents a handful of high-population urban centers from deciding every election. Abolishing it would make rural America politically irrelevant and undermine the federalist design where states matter as units. Direct popular vote sounds fair in theory but would actually concentrate power and make it easier for a candidate to win by running up the score in a few mega-cities.