1) stick = mock fighting - see Olympik Games & backsword & shin kicking etc - Yoemen practising, hand eye co-ordination - every Lord of the Manor had to provide fit men to fight - possibly a legacy from that.
2) Establishing rights to hunt etc - eg Abbots Bromley, illiterates (most people at one time) had to establish what and where to hunt, like walking (beating) the bounds of a town to define where they were - the locals all had visibility of where and who, once a year. Abbots Bromley horns have been carbon dated to 1065 - discuss.
3) Demonstrating how fit you were on May Day when the hiring fairs were taking place. Best dancers, fittest workers.
4) Black Faces - to hide identity - &/or referrences to Moorish - dancers would receive donations (food, money etc) like in the winter at Christmas but it was a form of begging, infra-dig.
5) Morris = Moorish or moorish from "mores and customs". tick both of the above.
6) Handkerchieves - ??? Bloody noses? see mock fighting.
7) Because it is what the English do - OK?
8) There is no one reason unless you ask only one person.

You might as well ask why line dancing
1) to give Morris dancers something to laugh at.
2) so that lone dancers can get up when they want to dance and not feel like a wallflower &/or have to run the gauntlet of waiting to be asked and then fielding suggestions based on a fairly obvious agenda.