Their chips "Loongson" appeared long before RISC-V is a thing in 2002, when MIPS is still widely used in the embeddeed world. I guess they just do not want to drop the experience accumulated in developing their previous chips.

and avoid the US backdoors into their military computers of course.

RISC-V is an open and royalty free ISA, it can't really be backdoored. And several Chinese companies are working on RISC-V implementation

From the wikipedia page for it[1]:

The Register reported in November 2021 the suspicion that LoongArch combines the best parts of MIPS and RISC-V, along with custom instructions.

[1]: https://en.wikipedia.org/wiki/Loongson#LoongArch

'silicon security' is probably as important as energy security.