Radiation has benefits that your chemical cytotoxics do not. An individual tumor often comprises of many subclonal cancer cell populations, all of which could have unique resistance mechanisms to allow that subclone to survive and proliferate in the presence of a single cytotoxic payload (say from an antibody-drug conjugate).
Targeting cancer cells with a radioactive payload can bypass many resistance mechanisms common to cytotoxic payloads.
Pluvicto (lutetium-177) is one of the hotter radioligand therapies as of late (approved for metastatic prostate cancer). Take a look at Fig 1a here - the responses can be quite striking for patients with extensive metastatic disease: https://www.frontiersin.org/articles/10.3389/fnume.2023.1291...
What I find most interesting are the supply chain challenges and logistics for radioligand therapies. Given the half-life of the payload, this is not something one can just manufacture and set on a shelf for the next patient. And of course the regulations involved with anything radioactive provide additional challenges.