My 2011 Subaru Forester, now a winter car, is a somewhat similar head scratcher. The beloved EJ series 2.5 liter engine in Subaru circles, was the standard in both N/A and turbocharged (WRX or STI) form for many years. Belt driven OHC and DOHC design. The Forester was, and I believe still is, built in Japan. In 2011 the Forester alone received a redesigned 2.5 liter engine, the FB series, with chain driven DOHC. Apparently, the chain drive allowed the valves and camshafts to be moved closer together for a more compact combustion chamber and consequently the cylinder bore was decreased slightly along with a slight increase in stroke. It did gain a few cc's of capacity, but still just under 2.5 liter. Rated hp was a wash but just a touch more torque. It seems manufacturers will go to great lengths for obscure reasons? In this case it would seem the chain drive and head changes could have been installed on the existing short block, but everything was changed. Go figure. All Subaru's received the new design engine the following year and beyond.
One detail that sprang from something in the new engine design was a sometime greater oil usage problem. It got bad enough that there was a class action lawsuit where the result was all warranties were extended to 100k miles, and if it was already over 100k, we had a limited time to bring the vehicle in for an oil usage test, which consisted of a dealer performed oil change and then customer to drive the vehicle for 1000 to 1200 miles and bring it back to measure the usage. Mine failed the test at over 180k miles on the clock so eventually I got a brand new short block at 183k miles. The only class action suit I know of that was more than just a token or a warning or other paperwork victory. It also got an airbag replacement later in the Takata air bag recall but that wasn't a lawsuit.