Part of the enjoyment of many trips, for me, is the planning. I get to learn about the city, see which places/activities I am most interested in, and gain some small level of insight into the location, the history, the culture, etc. I enjoy talking with friends about what we want to do while we're there, or asking what they liked last time they visited, so I don't feel a huge pain point here. There are certain aspects of travel I don't like planning, such as transportation, but that seems to be where travel startups have been most successful (booking flights, etc.)
Similarly, travel apps don't know what I like. A museum about a certain artist that I'm interested in? Great! A concert for a musical genre I don't have strong opinions on? Meh. And while the software could take my interests into consideration, inputting my preferences to useful levels of detail adds friction to the process.
Finally, I prefer my trips to be flexible. I rarely plan what restaurant I'm eating at; I'll walk around and see what looks good when I'm there. And if I see something near where I'm staying that seems interesting, I can do that instead of whatever I had planned for that afternoon. Travel planning generally strikes me as more limiting than freeing.
Perhaps there is something great that just hasn't been created yet, or maybe my travel needs are sufficiently unique that I'm just not the target market, but I'm not holding my breath.