Manufacturers made fewer inline six engines as they switched to vehicles with a transverse mounted, (crankshaft perpendicular to the direction of travel) front-wheel-drive engine connected to transaxle for front-wheel-drive. This restricted them to inline four cylinder engines and V-6 engines to fit it in sideways.
Vehicles with longitudinally mounted engines are mostly rear-wheel drive (exceptions being some of the older front-wheel-drive cars such as the Cadillac El Dorado and Oldsmobile Toronado) and were inline 6 engines, inline 8 engines (way back in the day), and V-6, V-8, V-10, V-12, and the rare V-16.
Manufacturers dropped the inline 6 except for some sports cars such as BMWs or Toyota Supras but as the number of all-wheel-drive automobiles has increased, a few manufacturers returned to the inline longitudinally mounted engine as it leaves more room for the driveshaft to the front axle without the need to raise the vehicle like conventional four-wheel-drive vehicles such as Jeeps, trucks, and vans.
The inline 6 in particular has the advantage of running smooth and doesn't require an additional balancer that a V-6 does. It's also significantly less expensive to manufacture than a V-6 or V-8.
Supercharging and/or turbo charging can be more efficient in an inline engine where the intake and exhaust are on opposite sides of the engine head, allowing a higher volume of air to pass through (air comes in one side and is exhausted almost straight out the other). V engines require more angles to move the air (in - down - out). The comparatively limited space on top of the V engine restricts just how much piping one can have (unless you want to drive around with a stack sticking up out of the hood like a dragster), whereas the inline engines have more horizontal space along both sides of the engine for wider diameter piping and thus more air flow.
An inline engine also accepts a single turbo well which keeps costs down compared to twin turbos found in V-6s or V-8s. While a V engine can have one turbo if one wants to get creative with the piping, V engines instead usually have two turbos - each connected to an opposite-side exhaust manifold (with all the increased costs).
Good points. To me the inline six has an elegance that sets it apart from other configurations. I’ve had two Supras, two classic BMWs, and a 1951 Chevrolet pickup all with inline sixes that were a big part of what made them enjoyable.