In addition to the other sibling comments, I think there's also a factor of greatly increased computing power. Back in the 90s and earlier, we just didn't have the computing power generally to encrypt everything with super-strong algorithms in realtime. This probably also affects who can practically do development work on state-of-the-art algorithms.
I recall, when it was originally created, SSL was a rarity, a thing only for the your bank account and the payment page for online stores, because nobody could afford the CPU load to encrypt everything all the time. Now, it's no big deal to put streaming video behind TLS just to ensure your ISP can't mess with it.
Does that really speak to why RC4 in particular, though? RC4 is a shambles due to algorithmic flaws, but it's not like it's export-grade cryptography.