Nothing closed source will ever be better than open source, in my personal opinion.

Also, online tools can disappear overnight. Better to have something that you can turn to without an internet connection and without them needing to fund their website.

Once I download GIMP, I am no longer increasing the cost of hosting the GIMP website by sending tons of data back and forth.

Photopea will eventually have to find a way to pay for their web hosting, which means eventually it will have to be paid for by something, either a fee or advertising.