Because all those things make it more palatable and acceptable to an American consumer who wants the ability to use cheap and easily available muzzle devices and magazines.  Having a bolt release is also a very good idea for any product in the U.S. market.

...and making it more palatable and acceptable to what are essentially U.S. standards would increase sales.

You don't have to like it, but ignoring that 1/2x28 tpi threads on a 5.56 caliber gun is essentially a defacto standard in the industry, especially the U.S.  firearms consumer market, as are AR mags on a 5.56 guns.

Using what is essentially a proprietary thread pattern (try buying 13x1L taps and dies) tremendously limits the options for muzzle devices, and especially the ability to mount suppressors which are readily available to the public in the U.S.  To boot, the use of a proprietary magazine from one source- Steyr, also limits the availability, especially as it did at one point about two years ago where Steyr got a major military contact that soaked up all magazines available for several months.  Of course for Steyr it is good on two points- they control the quality of their magazines which can help limit QC issues, and also it means they can essentially charge what they want as there are no other options (the Magpul AUG mags may or may not have an impact on the second one long term)

I know some of the reasons Steyr has not adopted these things as standard, and I understand those reasons (it has to do with the Steyr Europe and Steyr USA relationship and who calls the shots on product specifications) but that doesn't mean that it is the best decision for sales of the product in the U.S.  market.   A lot of European companies have a hard time wrapping their head around the U.S.  market, just as we Americans have a hard time wrapping our head around the European gun maker perspective.   Here in the USA we view that everything should be interchangeable, readily purchasable from multiple sources on a moments notice, and spare parts should be available to the consumer.  The European market just doesn't see it that way.