Passat sedan is discontinued because the trend towards crossovers and VW is investing towards EV more than anything and that's the reason they even discontinued their racing program.
Ford discontinued all its sedan lineup from US even being a US car maker but it will continue with sedans in other regions. Every market is different and VW US sales actually have grown in last few years, not declined.
As of global and particularly European sales statistics, I think you need to recheck your numbers. VW group was largest car maker in 2018 as well as 2019. Market wise it was also largest in Europe as well as China.