No, of course it's not rude to not acknowledge a dog. It may be slightly weird to completely ignore a cute placid friendly dog, but I would happily ignore a barky, aggressive, 'trying to jump all over you' type dog, that clearly has shit owners. (Well, I would TRY to!)
The problem is, 20-25+ years ago and earlier, any dogs that my family and neighbours and friends had, (including my parents, uncles and aunts) just used to come up to you, give your hand a lick, and let you pat their head for two seconds, and then they would go and sit on the couch or go in the garden.
NOW, you've got dogs who are absolute maniacs, who run up to you. pull you over, bounce all over you, and bark like crazy, as soon as you enter the room, or as soon as they see you if you're outside. A lot of dogs are more aggressive and bouncy and worse behaved than they were a quarter century or more ago. (NADALT.) NOT ALL DOGS ARE LIKE THAT.
DH's brother (who actually lives miles away now thankfully,) used to have a spaniel in the late noughties, and I refused to let our daughter into their house until they'd put him in the backyard or kitchen. He wasn't super aggressive, but he was very, very energetic and bouncy and jumped all over our daughter, knocking her flying, and scratching her and pulling at her hair. Did it to me several times too.
His brother thought it was hilarious, so I told them the dog goes OUT or we leave. So SIL (who was very placid) just pointed at the back door and told DH's brother to put the dog in there. Thing is, if he DID stay in with us, he didn't settle down. Half hour after getting there, he was still bouncing all over you, and scratching and barking. The problem is not the dogs though actually ... It's the shitty owners. DH's brother included. Dog had zero training.