Is it more foolish than the repeated instances of warships ramming one another in spite of the vastness of space?
The fact is, while one on one there is never ever ever a reason for a Gyrfalcon to close with a Hatchetman. But in a larger battle, there can be.
One weakness of mechs like the Gyrfalcon and the Vapor Eagle and others have is that while they're invincible dualists, some times in a battle you need to take a mech down fast, and sniper mechs just don't have the concentrated punch to do that. So if you need to kill some mech that's threatening to break your lines or finish off a damaged member of your star or lance, sometimes you do have to close in to ensure maximum accuracy, to draw fire away from a damaged comrade onto the probably undamaged sniper. Now, its been forever since I read that book (which was it? I'll go take another look) and I don't think Alex had a good reason, but that's not to say that there aren't good reasons in the context of a larger battle when your Gyrfalcon is the mech you have available to throw in at the last second to turn the tide, and being safe is no longer an option.