hpl - It's the result of investing a massive amount of time over the past few years digging through the AIM JS code and mapping to Kendo.
cishpix / jaymer - after reviewing the AIM code, the reason it's not working is that AIM doesn't use Kendo's out of the box method of export to xlsx.
To see what Kendo approach looks like, add this in the init script:
config.toolbar = ["excel"]
config.excel.allPages = true Note: config.excel = {allPages: true} is valid syntax as well.
Line 1 above adds Kendo's default button for exporting to excel to the grid toolbar (which is different than what AIM calls the toolbar.) See highlighted button in screen clip.

I expect that you'll likely want to use AIM's export button for UI consistency. To do that, AIM's export to excel method could be overridden to do it the Kendo way. There are actually a couple of different ways this can be done. Unfortunately that would take more time that I have to explain.