Mercedes, Jaguar switching to L6, Ford doing opposite

[SumoDog68]

It is never simple but in general most mainstream manufacturers have moved away from inline sixes. Main reasons are packaging , cost of production and flexibility of layouts.
That's not to say that inline six is not a great engine configuration - inherently balanced and easily up scaled to large truck engines . Torque is its strong suit - generally long stroke and don't rev as easily as some others .
Some of the best engines in the past have been inline sixes - BMW made their name with them , Toyota and Nissan in both road and off-road cars even Jeeps best engine is the inline 6.
These days they are replaced by nondescript boosted 4s that can be packaged in any driveline configuration and relatively cheap to make .
Some manufacturers stick with unusual layouts ( Porsche , Subaru ) but most follow common themes . Current fashion is small and turbo.