The Mystery of The Cretaceous' Songbirds
The short answer is that we will never know.
Luck can sometimes be a factor of who lives and who dies. But such an answer doesn't feel satisfactory given such a diverse group such as dinosaurs and other groups like Enantiornithes.

Together with hatchling specimens of the Mongolian Gobipteryx[35] and
Gobipipus,[36] these finds demonstrate that enantiornithean hatchlings
had the skeletal ossification, well-developed wing feathers, and large
brain which correlate with precocial or superprecocial patterns of
development in birds of today. In other words, enantiornitheans
probably hatched from the egg already well developed and ready to run,
forage, and possibly even fly at just a few days old.[34]
A 2006 study of Concornis bones showed a growth pattern different from
modern birds; although growth was rapid for a few weeks after
hatching, probably until fledging, this small species did not reach
adult size for a long time, probably several years.[37] Other studies
have all supported the view that growth to adult size was slow, as it
is in living precocial birds (as opposed to altricial birds, which are
known to reach adult size quickly).[26] Studies of the rate of bone
growth in a variety of enantiornitheans has shown that smaller species
tended to grow faster than larger ones, the opposite of the pattern
seen in more primitive species like Jeholornis and in non-avialan
dinosaurs.[38] Some analyses have interpreted the bone histology to
indicate that enantiornitheans may not have had fully avian
endothermy, instead having an intermediate metabolic rate.[39]
https://en.wikipedia.org/wiki/Enantiornithes

So we have this. Enantiornithes weren't completely bird like. They may have invested less energy in parental care. Perhaps taken longer to reach adulthood, longer to reach reproductive age. May not be as warm blooded as birds but not as cold blooded as a crocodile.  Maybe that is why they went extinct.
The Enantiornithes did not care much for their young, since they were born pretty much hardwired to be independent. This hard wiring probably worked find in a stable environment, allowing adult to spend more time and energy making more independent chicks. But in a hostile, changing world of post-impact, that was simply too much for a hard wired, semi-warm blooded chick. Especially one that took longer to reach reproductive age than most birds did. And birds by and large do invest in parental care of their offspring.
The answer is perhaps obvious if we could go back in time and observe the entire genera of Enantiornithes. But in the absence of a time machine and only fossils and estimated growth rates... we can only speculate.