A bit more information here to help the discussion. Firstly when considering AC bearings a traditional cup and cone assembly is a slightly different proposition to a AC cartridge bearing (ACBB). The ACBB can be dimensionally interchangeable with a deep groove ball bearing (DGBB) for example in a BB30 bottom bracket (7806 vs 6806).

Regarding preload;

1. All AC bearings need to be adjusted in an axial direction (from the side) due to the asymmetric shape of the raceways. This axial adjustment is referred to a preloading but only actually become a 'preload' once all clearance has been removed. Without some form of preloading AC bearings do not work correctly.

2. DGBB do not need to be adjusted in an axial direction in order to work correctly as the raceways are symmetrical. However the radial clearance in a DGBB also translates into an axial or sideways clearance too. Clearly when you are trying to control chain position for accurate gear section the presence of axial clearance is undesirable. This is why you preload DGBB in a wheel or bottom bracket - it is purely to remove the axial clearance.

Direction of forces:

The sideways (or axial) forces in bottom bracket bearings are negligible. The only axial forces are the preload that you can inadvertently apply through the adjustment system - so you adjust to remove the clearance and not to apply preload (same as a cup and cone).

In a wheel sideways (or axial) forces do occur during cornering. This is a percentage of the radial load it is supporting during normal straight ahead riding. The percentage is determined from the angle of lean and bit of Pythagoras Theorum. However even at significant angles of lean under high loading the axial forces are still lower than the radial forces. This is why many wheel axles successfully use DGBB.

So to summarise:
AC are not selected for bicycle bearings based on their ability to support axial (sideways) forces because the loadings are primarily radial in direction. Only exception is the headset lower bearing ;-)
ACBB offer a higher load rating than a DGBB of the same size.
When preloading ACBB, DGBB or Cup&Cone in bicycles the aim is only to reduce clearance to a minimum or a very light positive preload.
If you set up an AC bearing without preload control (or too much axial clearance) you lose the load rating advantage and get premature wear.