IE was the reference browser for the web in the 90s, and Chrome is that today.
I struggle to support iOS 9 (Safari 9) and I barely support iOS 7, because we have a number of users with old devices and we are not a consumer app so we can't just ignore our users who cannot upgrade their browser.
I regularly check caniuse and mdn to see if I can use a useful feature that is in Firefox, Chrome and Edge, and I regularly can't because Safari doesn't support it. Or often I try to use a feature and it is buggy on Safari. Safari is the only browser that regularly breaks our web app (most recently Safari 13 changes for the iPad desktop mode). I also see old versions of Safari in use by some of our MacOS users (presumably because they can't or won't update?)
If our users hit a show-stopping bug in any other browser (browser bug or our bug), they can usually try a different browser. But iOS users can only use WebKit, so they are the most vulnerable to serious bugs.
Our clients are businesses, and our users are their employees (from a wide range of backgrounds). The employees must use our web app, and our clients mostly don't get to choose what their employees use.
We log how many users are on old browsers, and we try to support users on old browsers if it isn't too costly for us to do so.
In my experience, the majority of people using a iPhone 4 or an Android 4.4 device are doing so because they can't afford to update, and they are often otherwise marginalised. I try hard not to give them yet another kick in the teeth for stuff outside their control.
It's not quiet that precise -- there was a transition period at the end of the 90s and a period of multipolar quasi-equanimity before Chrome's dominance -- but it's a decent first approximation.
https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...
I'm sure you don't have to support 9 years old Safari.
If Apple allowed alternative browser engines in iOS, the situation wouldn't be so bad.
Safari now is the only evergreen browser that does not support it.