Theres a reason to this I suppose.
Point being that "_" is often used to separate different words, as in, you cant have space in your variables, like you cant have a variable:
Therefore it is quite common that "_" is used instead of space.
Therefore there comes the situation where one might be wanting to select just one of those words, as for example, just the "ABC", by double clicking on top of ABC, user can select this single word from the whole things.
If you however Triple Click, you can notice that then the whole ABC_DEF_123 becomes selected.
So one click to get there, double click to select the single word, and triple click to select the whole thing.