Honestly, many other airline programs don't assign any seating privileges to the rest of the party. Flying Blue is just the status holder. Delta gives you a +1...but that doesn't work for my family of 5. Southwest will give you A-group boarding for everyone, but that will soon be "enhanced" to something else with assigned seating. So basically, Spirit is not much different here IMHO.

Now, when I fly Spirit, I always buy at the airport to save the $22 each way per person (adds up to about $220 savings per trip for me)...and they also always assign seats to my whole family for free at the counter. Sometimes I have to push for that, but they always do. Maybe it is to keep my young kids together with me, I am not sure why they do it, but they do.