There are companies who specialize in organising travel, which could be aided by better software.

Personally, I would pay for a travel planning app, but the pricing structure would have to be right since I'm not going to pay for a subscription for something I use infrequently.

I think the key thing here is that travel is already very expensive, so there is money to be made here in improving the process, but skimming some ad/referral revenue off a large volume is the easiest way to do so.

I looked for a travel planning app when I went to Mexico City last year and was generally not impressed with the offerings, so I just ended up pinning everything I wanted to do in Google Maps.