Why there is no high voltage repeater / voltage translator ic (like max232) for I2C
I am not sure if this question has a right answer, but the main motivation might be that I2C was conceived as a chip to chip on board communication protocol, and not as a "high distance" communication protocol.

On a PCB having somewhat high voltages lying around is quite a pain, plus each chip should include another voltage rail, and so on. U(S)ART is an RS232 derivative, i.e. it's RS232 with lower voltages, and that's why you can find the MAX232 and similar.

In the past the first difficulty that had to be overcome was "fast" and reliable off board communication, thus RS232 was born. It uses some +-12V I believe, and can go for quite a distance. Chips evolved, prices lowered and suddendly you have 10 chips on a single board, using RS232 is sub optimal because high voltages are not needed, and you'd need a port per chip on the main chip, or some daisy chain, or whatever. And here comes I2C: low voltage, multi device, two lines, faster, and so on.

I believe you can't find many voltages translators for I2C because I2C is not the right thing to use if you need higher voltages.