For me (as a beginner) the thing that has always held me back, without a doubt, more than anything else... is access to unfiltered sunlight and ground for growing. A large number of Americans live in larger cities where apartments, row homes/houses, or townhomes predominate. These larger cities are also the settings that are most likely to inspire a Bonsai interest. Casual interest by novices is often piqued in places like the National Bonsai and Penjing Museum in Washington D.C., Japanese Friendship Garden, Balboa Park in San Diego, the Bonsai Garden at Lake Merritt in Oakland. Most every uninitiated novice leaves these places wanting a bonsai tree. The majority of these (i.e. uninitiated) visitors, I would argue, are locals -- for example, Lake Merritt is not the first place tourists who have no familiarity with bonsai will go on their vacation to San Fransisco. They inevitably go home to their apartment or row house in San Francisco or on the Peninsula because...well...very few people can afford houses in this part of the world... and they try to grow bonsais on their balconies, on top of fences, on porches, in tiny gardens, or in the 4 foot or so walkway (if you're lucky) between homes .
I think more expert bonsai aficionados are less likely to be affected by these limitations because it really is hard to become expert working in these spaces. Although I did see a video on Ryan Neil at the beginning of his initial internship in Japan that showed his balcony full of specimen trees.
The push to give up is real when you have to be constantly moving and maneuvering your trees from one side of your townhome to the other, as the sun makes its way across the sky. I have a Monterey Cypress that is over 8 feet tall. In order for it to get both early morning sunlight and late afternoon sunlight to meet it's 5-6 hours of sunlight requirement, I have to carry it every day across rooms bent over so that the pot is below my knees and it still drags a good deal on the ceiling. Also if you're in a home where you share a wall with neighbors (like in a rowhome) the light on your relatively large 8'x12' back patio is never consistent throughout the seasons due to its proximity to your neighbors house or the single large pine tree managed by the homeowners association.
As a solution...I've thought about the option of ground growing trees in urban community gardens. I'm very hesitant to follow up on this though because every plot I've ever seen in one of these is dedicated to vegetables and flowers. I don't know how "neighbors" in these gardens would react to a Bald Cypress being grown to ten feet. I don't know how people go about setting up community gardens in large cities (in terms of permits, etc.) but maybe they could be set up specifically for ground growing trees with raised beds for the purpose of encouraging beginners. Another option might be a business (someone who actually has land in an urban center) where trees could be stored and watered for a reasonable price. Owners could then come in to work on the trees there. I don't like this idea. But maybe there might be some beginners out there that would actually like to see "their" tree get bigger, even if it's not kept at their private residence.