The 21xxxx.28xxxx,31xxxx,33xxxx all use the same camshaft part number so not limited to just your engine. But the main reason Briggs doesn't fix it is because it isn't as widespread as people think. Even if 100K fail every year compared to over 10M engines.
Unless you are one of the 100K. Like me, that's 100K that will probably never buy another machine with a B&S engine.