Why? 60fps isn't only about input response, games also look a lot better at 60fps with smoother looking animations and camera movement. And traversal/exploration still feels better, it's not all just menu based gameplay.
Besides they are charging a full $70 for a game that looks like it could have released on Ps3 with a few tweaks, the least they should offer is good performance.
Take a note from Falcom, their games might look dated too but they run great on Ps5. The Trails in the Sky remake runs at 60fps with good image quality and it even has an optional 120fps mode.