RC4 was fast in software for computers with weak CPUs (like 80286 or even 8086, which were still in use during the nineties) and no hardware assistance for cryptography. DES had been designed for computers that had a special DES hardware accelerator.

Moreover, together with RC2 it was approved for export from USA, during a time when this was prohibited, so it was included in browsers from the beginning.

When the export rules were relaxed, it was trivial to increase the key length of RC4, which could be chosen arbitrarily, so that appeared as a simple way to enhance the security of the existing Internet browsers.

This lead to its ubiquity in the early SSL.