We have them. The RAD750 for example (on the JWST and Curiosity rovers https://www.theregister.com/2012/08/08/mars_probe_cpu/ https://www.theregister.com/2012/

We have them. The RAD750 for example (on the JWST and Curiosity rovers https://www.theregister.com/2012/08/08/mars_probe_cpu/ https://www.theregister.com/2012/08/08/mars_probe_cpu/ ) costs about $350k, has the architecture of a PowerPC 750 (the blue and white PowerMac G3), and runs at up to 200 MHz.