You would not leave a young child to fend for themselves. And in many ways your mother has the same needs as a child.
How many people on here have had a toddler think it's time to get up at 3am?
The difficulty with an adult is that they are even less safe than a child. They are capable of putting a pot on the stove or getting out of the house at midnight.
This is for her safety.
Try not to feel guilty. My grandmother was in a similar situation. She would forget she hadn't eaten and when the carer came to cook a meal she didn't want to trouble him so would ask for a sandwich.
She spent the last two years of her life in a home, and it was a home. She put on weight because someone would help her to the table and ask which option she wanted for her meal and then put a plate in front of her.
My grandmother wasn't able to take advantage of the activities but the home had entertainment every evening, wine and chese, bingo, singing etc.
They also had trips out, to Blackpool for the lights with fish and chips thrown in (this was in Lancashire).
It really was a nice place to live, there were gardens and the residents could go out at any time, but accompanied by a carer.
When you were little your mum did what was right for you and your brother. Sometimes you wouldn't like it, you probably had a tantrum about brushing teeth or going to school or not being allowed to go somewhere. Your mum did things to keep you safe, it's your turn to do the same.
Go have a look at some places, get a feel, ask to talk to residents and staff.
The last time I saw my grandmother she reconised me and knew my name, but not the relationship, she thought I was married to my dad, and that my mum was a little girl.
But, and this is the important bit, she was happy, she was smiling and trying to flirt with the 25 year old partner of one of the staff.