Babies and young children are usually quite happy doing whatever it is they're doing right now. Any attempt to take them away from whatever that thing is can be met with tears and tantrums, even if it's something that's in their best interests, like having a bath.
Once you've wrestled with your child and got them into the bath, they'll be perfectly happy again - especially if they have bath toys to play with while they're in there. Now you have a new problem; you need to get them out again, and you're going to have to repeat the wrestling match. Children are contradictory by their very nature. It won't be long before you're plucking them out of the water and toweling them down whether they're crying and complaining about it or not! Top tip: Bribery almost always works.