Why only ball bearings on bicycles?
I think several of your assumptions are incorrect:


no high speeds: rim dynamos spin quite fast, up to 10,000rpm, and that does require effort on the part of the designers. Typically the drive wheel on those will have a radius of about 1cm, or a circumference of 3 1/3rd cm and 30 revolutions per metre. At 10m/s (30kph) that means 300rps or 18000 rpm. This is why they make such a high pitched whining noise when in use.
no high torque: a 100kg cyclist standing on a 165mm crank is exerting about 1kN at 0.165m, or 165Nm. That's comparable torque to a mid-range car. I repeatedly snapped a 8mm high tensile  bolt in the drive system of my four wheel load bike, and replacing that with industrial freewheels meant buying two of the highest rated units I could find (German conveyer belt parts rated to 250Nm)
No high loads: a touring cyclist with 50kg on the rear rack, plus half their 100kg body weight is putting a load of 100kg or 1kN on a 10mm diameter hollow rear axle. Those axles and the dropouts they bear on must be made of hard steel to stand the load, where the load bearing parts of a car or truck are typically made of much softer steel. 
Only ball bearings are used: modern sealed bottom brackets commonly use roller or needle bearings, as do many headsets. Internally geared hubs have used needle bearings for many years. Sheldon Brown describes roller bearings in his glossary, for example.


The answer is that various types of bearings have been used in bicycles and will likely continue to be. Again, Sheldon discusses needle bearings in Shimano hub gears from some years ago and they're still mentioned in the marketing.

One problem not unique to bicycles but especially relevant to them, is that more precise bearings are more vulnerable to grit and also to damage. So especially needle bearings need to be carefully protected from dust, sand, and forces outside their design range. Unfortunately doing that inside a suspension unit is hard, and last time I looked Cannondale had not solved the problem (my HeadShock is unmaintainable after only about 10Mm, I've seen multiple lefty shocks fail during a race because of light rain and fine grit causing them to abrade to uselessness very quickly)

But inside a hub or headset, for example, they can be amazing. I've talked to people who've ridden 20Mm on an Alfine 8, for example, with no problems.