Why do only hydrogen isotopes have separate names, deuterium and tritium, while other elements don't?

Because the neutron number of isotopes of other elements does not increase one by one like H, the neutron number of isotopes of each element is indicated in the upper right corner.

The English name of hydrogen isotope is:

Protium (prefix stands for proton)

Deuterium; (prefix means two)

Tritium. (Prefix means three)