Nuclear power requires a lot of water for coolant. Usually they use river water and release the heated water back in the river, which quite heavily disrupts the ecosystem.

Additionally, during heatwaves (which we're getting more and more of) the river water may get too warm to use, so the reactor has to shut down (happens in France almost every heatwave), which is bad as that happens when power usage tends to spike.

Nuclear is also extremely expensive, costs many years to build, not to mention we don't have enough educated nuclear engineers nor build capacity to keep up with the demand for new power. It's why investors generally don't bother with nuclear much, outside of specific niche cases. Not to mention the carbon footprint of building a power plant.

It's also likely going to get more expensive to run in the future. As renewables keep contributing more power to the grid (since they're so cheap and getting cheaper still), power generation will also fluctuate more. Meaning, other power sources need to be very flexible in when they output power themselves. Nuclear is famously quite inflexible, it takes time to spin up and wind down. There are reactor designs that are better at it, but even for those shutting down the reactor for a couple hours tends to be economic suicide as well. This exact reason btw is why gas is still used a lot; it's cleaner than coal at least, but also very easy to spin up or wind down without creating much extra cost. And it's much cheaper than nuclear (leaving more money to invest in renewables).

Nuclear could be great, if it was A) cheaper, B) faster to build and C) more flexible. And no, so far SMRs have not proven to be any of those things yet.