Trump took over the GOP too. Right wing media was initially against him. You can reductively dismiss this as him still being on the side capital , but Trump's trade policy is NOT what rich people wanted in general or else the US wouldn't have championed free trade for the last 70 years.

More to the point, building a national party with enough recognition to actually win is extremely difficult. Hijacking the Democratic party and giving people a reason to vote for it, difficult though it may be, is far easier.