I don’t doubt your explanation, but it’s tragic and backwards. It would make sense that a WordPress recipe blog wouldn’t be developed with smaller browsers in mind. But 5% of Instagram’s traffic is a gigantic amount of traffic, worth catering to. Wouldn’t it be the big websites that have both the budget and the motivation to make their sites work across browsers? This feels like a market failure.

Call me a luddite, but I think if I were BigCorp Website Director, I’d be saying “If you have to do something special to make it work in Browser X vs Browser Y, you’re getting too fancy, you don’t need that crap.”