Unless the copyright holders donated it into the public domain (fat chance), it's still under copyright for at least another 70 years.

Abandonware is nearly always technically illegal (after all, if it wasn't, and was formally released by the copyright holder, it would be freeware). As mentioned elsewhere in this thread, the game is still sold, so I'm not sure it even qualifies as "abandoned".

Most of these sites depend on the copyright owner no longer caring or being hosted in countries that may have shorter copyrights or aren't subject to the DMCA.