Before I start, although I say it was ruined by everyone most of them had little choice.
Top down
The BOEs: One thing that has been pretty constant through out my 15+ years in Japan. Most BOEs will choose the company that makes the cheapest offer. It sucks, but it's true. There is also a culture of switching out companies for one of the competitors every contract cycle because they have had problems with the quality of the cheapest possible deal they could get. (No surprises)
Dispatch Companies: Most dispatch companies have lowered the cost of the ALTs by constantly reducing wages and cutting benefits. Thus attracting fewer and fewer first language speakers and even fewer qualified teachers. They also don't want to spend money on training because they know that cost is the main interest of BOEs.
Schools: Due to the high turnover of ALTs they see little point in training ALTs in teaching skills or letting them know the details of individual students needs. Due to their part time contracts they see ALTs as outsiders and make little effort to accommodate them.
ALTs: Most ALTs are paid so little and given so little respect that they have lost the will to work hard at their jobs. Even the ones that make the effort, often have their efforts brushed aside by the schools. Also, the dispatch companies do sometimes offer the chance of increased salary but only to the ALTs that excel not across the board so ALTs are discouraged from sharing their work/materials.
How can we change this system? As ALTs we can go above and beyond our job description and actually try to learn about education and offer teaching ideas in the classroom. We can also make efforts to befriend our Japanese coworkers and make their life easier. In the end, you will get recognized and eventually might get a direct hire or better job. Stick at it guys! You can do it!
TLDR: The system is broken but it doesn't mean we have to give up.
by Vampyrebyte