The reason is because DL does not consistently apply their bulkhead rules and they constantly screw over people with actual disabilities (or infants in arms) who show up at check-in expecting to get such a seat because that is what they have been told they can do and they just don't know any better. Even people who do know better (me) but choose not to lie to obtain one of these seats dishonestly and instead assume that when bassinets are available bassinet requests will be honored (silly me) find themselves screwed over by DL's not enforcing their bulkhead rules.

Note that opinions on this point differ on FT. For example, OrangeCountyCommuter thinks that all those people have disabilities that are not visible. LMAO