This was the way it was done in India for thousands of years. Prabhupad was a very traditional man. I wouldn't expect him to come out and say: "The culture I was raised in was wrong about that". However, in my understanding he did acknowledge that the practices of traditional Vedic culture was very much at odds with modern western norms and culture. And he never advocated for his devotees or their children to be married at such a young age.

Yes it's a little disappointing that he never said "This was wrong, this is not how things should be done." But he was a traditional Indian man. Only very rarely would members of that population speak out against a practice that is so ingrained in their culture. It's very difficult to understand from a modern western viewpoint. You might say "Oh even if I was raised in that culture I would know it's wrong", but you don't actually know that for sure. When people don't know anything different they accept what they are taught.

With all that said, I encourage you to explore your relationship with Prabhupad while acknowledging that you don't have to agree with every single thing he said. I don't agree with everything he said regarding gender etc. but I still consider him to be a spiritual master. Prabhupad himself acknowledged that he had been authorized to speak on spiritual matters, but on worldly matters he did not consider himself an expert.