Tarot for the 21st Century!
In my personal experience, I am designing my deck because I am having trouble with imagery and thematics which speak clearly enough to me that I can read accurately for others. I want to be able to look at the cards and spread and be able to tell a story to my querent which can be applicable to their situation and they can use to gain insight to overcome their difficulty or settle their own mind. I would submit that many people would seek to help others, and produce their decks to do so. It may be that some produce theirs to earn a living, but who are we to judge that? If one has a talent, why should one not get paid to utilize it?
The number of decks out there represents a diversity of thoughts and approaches, I would suggest that this actually benefits the community, since it allows one to find a deck which strikes a chord within them and that they can be comfortable with reading.
Tarot is the emblem of a journey, Taoism teaches that there are many ways, each person has one. Each deck is a path. Whether one goes along the direction someone gave them, but still journeys on their own, or forges their own path, and blazes the trail for others to follow, tarot is never diminished. Potency of Tarot can neither be diminished, confused or enhanced, since Tarot is never in the deck itself, but in the reader's understanding of the cards.