This might be a question for Steve specifically, but it was recently brought to my attention that a single jump tender can move other ships in both directions through a jump point without ever moving itself. Is there a reason that permanent jump point stabilization is one-way, but temporary jump drives are two-way? It seems like they should operate in the same manner, whether that be one-way or two-way transit.
It's because it's assumed that the ship is moving back and forth across both sides of the jump point to escort any non-jump ships through.
Given that the alternative is that you'd either need to move the jump tender back and forth manually or need twice as many ships; it's a clear quality of life improvement.
Stable portals, on the other hand, offer tactical advantages when you have to secure each side individually - it means, for instance, that a fleet without tenders cannot jump back across, which can either be an advantage (the enemy can't cross over to your space as easily) or a disadvantage (your fleet is now stuck in a hostile system.) Also, keeping the stabilization ship safe for 180 or 360 days can potentially be an important consideration (the AI certainly worries about, and viciously protects, its stabilization ships.)