Why do red kidney beans come in 410g cans

This isn't the "quick" nor the healthy answer, but I personally do a twice-cooked system. I leave the juice from the can in the mix, and boil it down, which takes 15 minutes or so. Retaining the flavor of the canned fluid is essential, in my opinion.

Then I "fry" the dry-ish mixture which is beginning to separate in maybe 1 tbsp preheated lard per can of beans, stirring a lot at first. Lastly, very slightly simmer this on low heat for 1 hour or so, stirring occasionally. Flavor is awesome. Any kinds of beans can be prepared in this way, and it is similar (varying on oil and legume variety) to other paste concoctions created elsewhere.. such as in the middle east.

Note that this method negates the need for lots of "mashing". So, if you're more looking for less effort, than necessarily for "quick".. this could be your answer :)

Adding a little bicarbonate of soda (baking soda) to the beans when soaking overnight should help soften them.