Because 99% of the time building images for Arm processors is a pain in the ass. It's not just about making sure you have all the requirements lined up, but the

Because 99% of the time building images for Arm processors is a pain in the ass. It's not just about making sure you have all the requirements lined up, but the processors themselves are pretty slow when compared with a relatively modern Intel CPU, so builds take way longer. Compiling Tensorflow, for example, can take days on a Raspberry Pi. Source: my company has to build software for Arm on a regular basis.