Official JEDEC specifications are that DDR4 is 2133mhz. Motherboards should always initialize ram at the JEDEC spec unless there is manual user intervention to enable an XMP profile - that's intended operation.
XMP profiles are Intel's officially supported way of settings speeds beyond JEDEC which are supported by the CPU and Chipset. Keep in mind that anything beyond Intel's own officially supported speeds is considered an overclock of the IMC (Integrated Memory Controller) of the CPU.
Also keep in mind that some vendors motherboards may additionally enable a CPU clockspeed overclock (and subsequent voltage increase) when you enable XMP - on Asus boards specifically this is called "MCE" or Multicore-enhancement. This was revised during the period of Skylake via BIOS/UEFI updates to warn the user of this and ask if you wish to use stock Intel operation - but only on more recent boards have they made the language more clear about it.