Because these guys are merchants.
They'd apply coroporate thinking to their defense plans. Instead of having a big navy, they'd have a gestalt defense network... very organized and beauracratic, everything assigned by dollar priority and blah blah blah...
Which would explain why so many worlds have no TEC presence. They aren't worth properly defending, unless they totally submit to the authority of one of the major players within the TEC (ie: Haliburt--- ahem, Tondam Corporation takes over for the good of the species, eliminating rivals and expanding their holdings while they're at it... in the name of the TEC; all perfectly legal of course... times of war being what they are).
The TEC are not some big noble 'save the humans!' effort, they are a bunch of major powers who had the foresight and gumption to form military assets, forge business alliances, and respond to the threat to their profits. Want the plans to a Kol? Sign over your sovereignty or a large share of your profits (etc..) to become part of the TEC so that you can defend your people... and who knows, maybe even absorb a nearby independent colony or twenty in the process.
Mind you, that's not what the broadcast centers are transmitting.