why is there no small android phone
Sony Xperia Z3 Compact is 4.6", but super brittle. The Huawei P10 is 5.1" and has a case that makes it a tank. The SOYES XS12 Cell Phone is 3.0", if you need smaller. Have you searched using GSMArena's phone finder? https://www.gsmarena.com/ https://www.gsmarena.com/results.php3?nHeightMax=135&nDispla...
So for current small android phones I'm guessing the unihertz Jelly 2 is one of the few remaining.