Again, because Ainge probably thinks Smart is significantly better than you think he is.
You know you're allowed to negotiate a long term deal even if a guy didn't get an offer sheet, right?
Nurkic didn't get an offer sheet, Aaron Gordon didn't, Dante Exum didn't, yet they all signed long term.
You don't have to hold your breath and say either offer sheet or qualifying offer only if you actually want to keep the player.
Those aren’t the only options but in the scenario you lay out the point is to have Smart around to maximize winning potential this year, have him as Kyrie insurance next year and gamble that his contract is movable next year if Kyrie stays. There is really no need to take that gamble because Smart has no suitors so they’re guaranteed to have him this year; they have Rozier as insurance if Kyrie leaves and by my rough math will have somewhere around $12-15M in cap space to find a 3rd guard (depending on how many picks convey and how high they are). Also while flipping Morris is probable anyway, as a solution to the tax this year it really requires a team with cap space to take him without sending any salary back and there aren’t a lot of options (only the Hawks, Kings, Bulls, and Mavs can absorb him right now) Edit: I forgot about trade exceptions, there are actually a lot of teams that can take Morris for no salary. Short of needing Smart’s salary for a bigger trade and not having it, the best case scenario for the Celtics is Smart on a cheap one-year deal to delay the repeater tax and then if they want him long term they can make the best offer next offseason (when his market will also be soft IMO - regardless of views on his value, his skillset just doesn’t get paid on the open market).
Just from your examples, Nurkic and Gordon are starters and Exum at least you can squint and say maybe the injuries have hampered his development and maybe if he stays healthy he can make a leap. They also all play for teams that traditionally have had difficulty keeping guys when they hit UFA or attracting free agents without overpaying. Smart would be the 3rd guard On the Celtics (and arguably the 4th most valuable given Rozier’s leap and his role as Kyrie insurance). It doesn’t matter how good Ainge thinks Smart is or what he values him at in a vacuum, if Smart can’t get any offer on the open market why should the Celtics bid against themselves?
By all accounts they negotiated for a longterm extension last offseason. With Smart declining the extension and going on record after the ECF as feeling he was worth $14M+ per year, the Celtics have a pretty good idea of what he thinks his value is, and appear more than willing to let the market prove otherwise. This definitely reminds me of IT’s Brinks truck comments - and for the record I have no issue with IT or Smart wanting to get paid a lot or publicly talking about it. But when you talk to reporters about how much money you want, you shouldn’t be surprised when your team takes it at face value and acts accordingly.