It's moreso that the half-life of both natural uranium isotopes is very long; billions of years. When something has a very long half-life, it emits fewer energetic particles per second, and inflicts lower dose (energy deposited), and therefore lower health risk.

All the daughter products are in secular equilibrium and so are also "rate limited".

When you split uranium nuclei in nuclear chain reactors, many of the resulting "half-uranium" fission products are neutron rich, and have very short half-lives. They quickly decay towards stability and along the way shoot out lots of radiation very quickly. This is high-level nuclear material and is dangerous.