Until just a few months ago I'd never ever heard whispers of attachment theory being used with adults (and I've taken a helluva lot of devPsych classes). It does make sense that there can be valid applications of it with adults, especially dealing with early childhood trauma, but at most it would only be a small facet of the overall picture. Hell. In Early Childhood Dev. it's only one facet of a facet. A very fluid one, at that... Because the same enfant (0-2) can have different attachment styles with different people, in different scenarios, & situations both at the same time, and over a period of time. But attachment styles / attachment theory? Still only 1 small part of normal attachment / bonding / self awareness / discretion / etc. in stages of development. It's a piece. A rather small one, at that, and it doesn't apply to everyone ever, much less always.
Something very key to know... Developmental Psych is the softest science, in an already soft science (psych). There are huuuuuuuuuuge problems with many if not most of the practice & theories
(Developmental psychologists are usually the first to admit this! They tend to be a very quirky bunch / very adaptable. Although I'm sure it comes with the territory when there are 6 theories for the exact same thing, and they're all right / all wrong / it only matters on a case by case basis so wheeeeeeee! I mean, can you even imagine working in a field where the possible answers for 6+4 include, 9,11,207, kittens, if in the presence of a tribe of red clad warriors turn to page 60. Wait! Page 60 of what? We're not telling. Figure it out.)
... Not the least of which being sociocultural issues that flat out negate at least 1/3 of the "best" theories. Like, if A then probably B or C... Works in North America & Northern Europe... Most of the time. But the exact opposite is true in about 1/3 of the world, and in another 1/3 of the world (insert 50 different variations). LOL I have a good friend, PhdPsych/Dev.Psych, who runs around the world disproving well held theories. Started on accident when she wanted a paid vacation to Bali, so turned it into a research study. Come to find? Half the things that are held as true for western babies, are total bullshit for babies from cultures that don't set their children on the ground until 1-2 years old. Same is true with most DevPsych theories. Absolutely true! Sometimes. In some cases. In some areas. But not at all, or maybe only partly true, if you leave your sociocultural niche.
So whenever you're looking at developmental psych? Large grain of salt to begin with, and then know that human development is so complex, that there is no single unifying theory that applies to everyone. Far more often, we're looking at hundreds of facets / hundreds of theories / that goes into each child & adult's progress through the lifespan. A lot of which are conflicting, and most of which we only have vague attempts to describe.