There are automobiles with CVTs. For bicycles the efficiency, weight, complexity are issues. Probably the biggest issue is need. Really, 27 or 30 ratios are plenty. If you really must have more 90 isn't too hard to get to. (SRAM dual-drive hub with 3x10 drivetrain). You can spin at 80 RPM now, you just may have to go a bit slower than you'd like!