You're trying to draw a comparison between app developers supporting multiple CPU architectures for their applications, and web developers continuing to use JPEG and PNG files for their web sites. I honestly just don't see how this comparison works.

Adding support for a CPU architecture is often a considerable amount of work, and the pay-off is often small, although this of course depends on what kind of software you have. For typical applications for end-users the cost/benefit ratio for supporting anything other than x86 is typically very low. For other types of applications like servers it's higher, so they often do support arm, s390, ppc, etc.

Supporting jpeg however is very low cost, with very high benefit: about 20% of browsers don't support webp. It's a small nuisance, not a substantial amount of continued investment of work like supporting a new architecture.

If 25-50% of your users used RasberryPis to run you app you’d support it properly.

Itanium failed, in part because it broke compatibility. AMD succeeded with x86_64 precisely because they realized that supporting the programs people actually used was vital.