What are Ash's companions' reasons for following him?

Can someone list of reasond for why every person that Ash has travelled with, decided to follow him specifically.

We all have an idea for the writers' reasons for lumping all these characters with a 10-year old beginner trainer. We all know Misty's reason for following Ash *cough*bike*loan-shark*cough*, but what are the reasons for the other characters. Heck, we can even question why they became such good friends in the first place and decide to follow him. And if that's the case, why haven't other characters joined (or stayed with him for the whole region).

Ash's companions:
Misty
Brock
Tracy
May
Max
Dawn
Iris
Cilan
Clemont
Bonnie
Serena

Temporary/Considered:
Todd Snap
Sakura
Cheryl
Buck
Alexa

Usually when a trainer goes on a journey, they usually travel alone with a party ranging from 1 to 6 party pokemon. It is never required for other people to join that person.

Misty - Wanted her bike and eventually just wanted to stay with him somewhat.
Brock - He just loved how Ash was with Pokemon and decided to follow him because he wanted to travel, but he had family problems.
Tracy - He wanted to eventually meet Prof. Oak.
May - Bike and wanted to travel.
Max - He wanted to travel because he wanted to see how Pokemon Trainer really were.
Dawn - Bike and wanted to travel
Iris - Cilan suggested all of them to travel together and she found Ash interesting.
Cilan - Wanted to study the bond between Ash and his Pokemon.
Clemont - No reason was ever really given though he wanted to leave the city for some reason and he liked how Ash was with his pokemon.
Bonnie - Wanted to stay with her brother and find a wife for him.
Serena - She wanted to meet Ash again and give him back a cloth that he had given her at a camp. Ash then suggested her to travel with them and she agreed.



Todd Snap - He wanted to take pictures of pokemon.
Sakura - I don't recall her ever traveling with them. They were just hanging out when they were in town.
Cheryl - Ash and then said they would help her find the Combee nest.
Buck - Ash and the group wanted to help find the treasure.
Alexa - She was going to Kanto like Ash and then and just stuck around for a bit.

The only quest remains is why other characters never followed Ash & Co (they really need a name). Such as: Gary, Ritchie, Bug Samurai (the first trainer after Misty), so many rivals from Hoenn, Sinnoh, Unova, etc. They travel alone for some reason.

And most of these companions did not need to travel with Ash to fulfill their wishes.

"All on your own? You should rely more on friends. Don't try to be more than you are. Be yourself and ask Ash for help." (Sonic Rush in 7 minutes)

I assume they follow him because they are naturally attracted to his aura and want to be around him

I always thought it was a little weird and out of character for people to just drop their lives and travel with Ash, but I guess traveling with friends is a lot better than traveling alone. I always imagined it would get incredibly lonely being out on the paths all by yourself. Not to mention scary at times. I guess you have your pokemon with you, but they aren't the best companions for holding a conversation with. :P