Decapods had their following, reason being they could spread a lot of weight and tractive force out over light rail. Ever hear of the Russian Decapods built here in the US for the Czarist government in Russia during World War One? The Russians puchased them just for that reason. So if you were a 'road with light rail and needed something with more pulling power to use on that light rail a Dec wasn't a bad choice.
Of course, the Pennsy Decapods were so big and heavy they'd have crushed everyone elses rail to powder, so why the Pennsy went the Decapod route is kind of a head-scratcher.
The Russian Decs that didn't make it overseas due to the Bolshevik Revolution were sold at bargain-basement prices to several American 'roads, the Erie, Seaboard, and Frisco spring to mind. They were well-liked too.
I like Decapods, those ten-coupled drivers are just so cool!