You've received good explanations but, IMO, not so much when it comes to instructing you how to take a better photograph.
On the other hand, all you asked for was an explanation, not a lesson.
Sort of like learning how to play, let's say, tennis.
First shot ever hits the net.
"What did I do wrong?"
"Throw the ball higher."
"Put your left foot more forward."
"Get on the ball of your foot more."
"Shift your weight earlier."
"Don't take your eye off the target."
etc.
Second shot goes out of bounds to the right.
And then comes the inevitable, "Buy a better racket."
"Buy better shoes."
"Buy better tennis shorts."
Obviously, I have no idea how skilled you became with your earlier photographic experiences. However, let's now say you had played the piano when you were young and you've decided to play again at age 68, after a lay off of some forty years.
Yes, the keys are all in the same place and you can name the chords in a Major chord progression but you probably cannot play even as well as when you stopped playing all those years ago.
You are out of practice and, as the saying goes, practice makes perfect.
Maybe you learned the piano by only learning where the keys are located for each song and never really learned how to read music or understand the construction of music. Maybe that's your current approach to re-learning photography.
If so, have at it.
Otherwise, don't be concerned about your first song or your first few photographs. Rather than asking why your first shots weren't perfect, simply dedicate yourself to a re-learning process that will educate your memories and provide a few insights into the particular, and sometimes peculiar, aspects of digital photography.
More than likely, your technique for shutter release could use some brushing up on. Your ability to hand hold a camera for longer exposure is probably not as good as it once was.
Maybe your grasp of the exposure triangle doesn't inform your memory of how the three legs work together.
Your new camera has many more features and functions than your last camera and, if you do not comprehend their operation along with how to quickly and accurately set them (or defeat them in some cases) into the camera's operation, then you are not going to succeed at your new hobby. Look at where your focus points were vs where your subject was.
And, certainly, digital ISO is no where near as simple and as confining as it was when film was the only available medium.
As if you were learning to play piano once again, pull out the most basic lesson plan and start afresh. Realize your first attempts will not be the best by any standard.
Look through the archives of the forum for suggestions on how to acquire the skills and knowledge required of a decent photographer. If you knew the basics at one time, they aren't that different now.
What's changed is you.
But asking for advice on one or two shots is only going to help if you could go back and redo those shots. And you can't do that.
Each shot will be unique and that's where your learning process should take you. You can make the same mistake numerous times, but each shot is not the same as the last or the next.
Gaining an explanation of what went wrong then is not as useful as knowing - on your own - how to make the shot better the next time.
Patience is a virtue. How's your patience?