I know what you mean - I think it is the shock of moving away from when they actually needed you, the enthusiasm they used to have when they were small. I miss them being excited about puddle jumping and going for walks. Now my children are typical teenagers and find anything I want to do boring and are glued to their phones. Doing anything as a family is tough when three are teenagers and one is almost a teenager (and toddler), they all have wildly different interests and just getting them out of their rooms is a big deal. It is sometimes so difficult to get them out that it isn’t even worth the effort (all they do is whinge).
I know it is just a phase, but it is tough. I miss knowing what they are thinking - when they would tell me everything. I miss the days when they were young, and now I feel disconnected. I know it is the natural order of things - I was also the same with my mother growing up, when I resented being forced to visit family. But it is still makes me sad.
Think of it in another way - you are a great mum because you have encouraged your children’s independence. This will help them in the long run.
Nowadays, my toddler keeps me company and is quite happy to spend time with me, but before her birth it was really really tough.
I would suggest picking up your hobbies again, or finding what makes you happy. It is a tough time, but it can also be a great time to re-discover yourself again, to re-visit the time before the children were priority. With teenagers being more independent, it is possible to enjoy dance classes, piano lessons, sports, arts, social groups - the world is your oyster.