If buying a SPIA to establish a floor was anywhere near a neutral expense, more people would do so. There's a high probability you will pay a substantial premium for the payout your SPIA will provide, especially at present interest rate/yields. That premium, and forever limiting your options after buying a SPIA (a big chunk of $ is gone), is the reason buying an annuity doesn't make sense to many, though it may for others.
Even those (self included) who never plan to buy an annuity, might if their nest egg falls too far too soon. I'd consider an annuity only when/if my nest egg starts to approach my
annuitization hurdle at any given age. Linked here several times
http://www.schulmerichandassoc.com/Modern_Portfolio_Decumulation.pdf
Most here didn't retire at that threshold...
People who retire at/near or below their
annuitization hurdle may indeed be best served by a SPIA. Otar is another discipline like Pfau.