Some toddlers remove their diapers because they are uncomfortable in the diaper or they may be ready to potty train and not want to wear diapers anymore.
Some toddlers decide one day that they are gonna stop wearing diapers and then go to the toilet.
My nephew did that same thing when he was 3 years old.
He took off running to the bathroom and then took his diaper off and went to the toilet.
His mom and dad never toilet trained him and figured he would decide on his own that he wanted to go to the toilet.
He no longer wore diapers after that.
However it does not always mean that the toddler is ready to potty train when they take off their diapers but it can be a sign of potty training readiness.
But if your toddler is not going on the toilet but still removing their diaper then you can take some clear packing tape and wrap the packing tape around the toddlers diaper.
The packing tape will keep the toddler from removing the diaper and also keep the diaper from sagging and drooping as well when it gets full.
If your toddler is taking their diaper off then you may need to change them more often unless the diaper is a dry diaper.