As much as I love to dunk on the Dolphins, there is a logic to this.
Tua has a massive cap hit from his 5th year option. The Dolphins are just as over the cap as we are with even more valuable pending free agents, but while we have the luxury of kicking ~20M down the road on Allen's contract the only way they get to mitigate that hit is with an extension. And that means paying the going rate, purging some of your best talent or cutting bait and trying a QB from scratch.
I didn't say it was good logic, and their situation is self inflicted, so I am enjoying their pain.