I said it had been a long time since I was involved with autoland development but I was curious enough to dig a bit into those distant memories. AC 120-28 is the "bible" for autoland systems development. The current version is D and it, and the related appendices, can be found here -
https://www.faa.gov/regulations_poli...cumentid/22750
Autoland certification uses simulation to demonstrate performance under a huge range of conditions. The flight test program has to produce sufficient data to show that the performance of the aircraft matches the performance of the simulation. One of the inputs to the simulation is the wind model that is defined in Appendix 4. If my interpretation is correct that wind model does not produce headwinds that exceed about 26 kts.
It seems likely that the autoland wind limits are set by the wind model.