Instagram hasn't updated its web application in years -- leaving out the filters which I don't use, unfunded Mastodon has an easier, faster and more reliable interface to upload photos.

My experience is a bit different. They constantly update it and make it more unusable. At this point it's totally broken. Occasionally I open it, it loads for 30 seconds, I have a notification icon for a post I saw a month ago, then my feed shows the same picture of a guy I follow driving his rally car, which was posted several months ago, then I log off. It's truly bizarre what they've managed to do.