Reached out to an ex after 15 years, need advice

I reached out on FB to an ex from 15 years to see how things were going. She messaged me back with 90 minutes, sent me a friend request which I accepted and then we real time messaged with her asking me a ton of questions before I had to end our conversation since I had to be somewhere. Two weeks later she messaged me and we exchanged a couple of messages, but not in real time and then I asked if she wanted my number. She said yes and then 4 days later on a Saturday morning she messaged me asking what would be a good time to call during the weekend. I messaged back Sunday morning to call me any time after 5 pm Sunday. I never heard back and 10 days later, I messaged her to see what was going on. Four days later she messages me stating that she didn't get back because a couple of relatives had Covid and asked how I was doing. I responded back within 90 minutes to say hope everything was ok and I was home if she wanted to call. She never did and that was that. I wanted to get some advice as to what possibly happened. Why would someone respond to me quickly, send me a friend request, ask me a lot of questions and then later on ghost me?
I don't get it and am a little confused. I was really hoping that we could have rekindled something and I keep thinking that if I got back sooner on that weekend that she would have called and maybe we would have met and maybe something would have come out of it but this was months ago so I know there is no hope, but I am still confused. Would like any advice. Thanks