Fact is, there just aren't many places for him to go. Just a quick run-down of teams in the West, East right now. Also not certain who has the money to sign him, just looking at situations:
Warriors- Nope
Spurs- Would be super interesting, but they still have Parker for 2 more years. Won't move on from him unless he retires with Duncan.
Thunder- Nope
Clippers- Nope
Grizzlies- Possible, but he won't be there first option. They'll want Conley back
Mavs- Hell Nope
Rockets- Nope. Rondo is an anti-Morey ball player. Also they won't be looking for another ball-dominant PG for a long time next to Harden after the Lawson fiasco
Blazers- Nope
Jazz- Very Possible. Need a PG upgrade, but also Exum coming back next season. Might not want to commit big money to a PG
Kings- Yep
Nuggets- Nope. Mudiay is there future
Pelicans- Nope. Have 22 mil committed to Jrue and Tyreke next season. Unless they traded both, which seems unlikely, Rondo doesn't seem like a fit
Suns- Bledsoe, Knight, Goodwin. Too many bodies here for Rondo
Wolves- Nope. Made a long-term commitment to Rubio for the next 3 seasons.
Lakers-Possible, because it's the Lakers, but I doubt they want Rondo crowding the back-court for Clarkson and Russell. Far more likely they spend their money elsewhere in FA. Also doubtful Rondo would commit his last contract to a major rebuilding squad.
East:
Cavs- Nope. Kyrie in place
Raptors- Nope, Lowry in place
Bulls- Very possible, but still have Rose at 20+mil next season and they might want to look at getting Jimmy more playmaking opportunities. Can see this as a viable destination
Hawks- Nope. Teague signed for another season and they'd just turn the team over to Schroeder anyway. Not a good fit.
Celtics- Nope. IT and Smart in place.
Heat- Nope. Committed big money to Dragic last off-season
Pistons- Nope. Committed big money to Jackson last off-season
Pacers- Possible, but very unlikely. Doubt they want to recreate the Rondo-Monta pairing and Hill is signed on for next season.
Knicks- Very possible. Need an upgrade at PG and will want to bring in another big piece to pair with Melo and Porzingis. Big market
Hornets- Nope. Kemba's there guy
Wizards- Nope. Wall in place
Magic- Nope. Payton in place and Dipo would take over for him if they moved on from Payton. Not the right fit
Bucks- Possible I guess, but seems like an awkward fit. MCW already in place.
Nets- Possible, but they might want to rebuild and ship off their few good veterans, rather than try and retool to be an 8th seed. They'll have the money though
Sixers- Nope. They'll deviate a bit from their rebuild plan with their new FO guys, but I doubt it'll start with a max deal to Rondo.
Could be wrong on some of these situations, but the only teams who I could see having any serious interest in Rondo are the Jazz, Knicks and us. Pretty much everyone else is already set at PG.