With many XC models I was looking to buy the 27.5 tires were provided only on the smaller frame sizes and probably to provide a somewhat lower standover height for riders. The Scott 965 I bought was only available as a 29. When it comes to tires there are the most options with the 27.5 at this point in time but a few years from now the situation is likelly to be the reverse.
With the ongoing shortage of new bicycles in the inventories of bike shops, the choice becomes what is available unless one does not mind waithing until next year and hopping for the best. The best available XC bike in my size and in my area was the Scott Scale 965 29er and that is what I bought.