the breaking up has been going on for a while, e.g. Canon bought their medical line of business back in 2016.
Westinghouse negotiated fixed price contracts to construct nuclear reactors and Toshiba provided financial guarantees, so they ended up on the hook for massive cost over-runs. In 2017 alone, Westinghouse reported an annual loss of $9bn. and declared themselves bankrupt.
Toshiba had to sell a load of businesses over the years to escape the Westinghouse black hole and repair their balance sheet.
Cameco is the second largest uranium producer in the world. Brookfield Renewable Partners owns and operates a lot of power generation. Both are Canadian where there is a huge pool of both power generation and specifically nuclear power generation talent and experience. As an example until 2016 Canada had the largest operator nuclear power facility in the world, several provinces are currently in the planning phases of SMRs, and Canada will be financing CANDU reactors in Romania.
It's safe to say they see some sort of advantageous vertical integration of the supply chain, as well as believing regulatory and economic outlooks being good.