"How can someone still be playing Java games on classic mobile phones when there are so many interesting 3d Android games one can play?"

It is like asking how someone still be playing DOS games on old hardwares (IBM XT, 286, 386, 486, Pentium 1)?

For fun. For nostalgia. For the feeling. For the atmosphere of the games. Because I (we) enjoy them. These games are sometimes/often better and more enjoyable than the fancy 3D games nowadays.