The English language has lots of rules, nuances and exceptions. While therapeutics is a noun, it can also be used as an adjectival noun - when "the" is before it, it is almost always used in the adjectival form.
The therapeutics institute
The therapeutics conference
The therapeutics forum
When "the" is used before it, the native English speaking ear is anticipating the subject noun which is what makes this sound awkward. If you expect the listener to use .com as the subject noun, that kind of works as a domain hack, but most people are not going to get it.
Similar terms like TheMathematics and TheEconomics are registered, so you are not alone in your line of thinking; however, awkward names can be a tough sell.
Good luck with it.