There are more layers, if you'd like to look into it.

- Web developers don't support older browsers because they lack the skill and economic motivation for it.

- The managers of web developers will not support them, because there is no money to be made in supporting older browsers. Nor are there career benefits in maintenance projects. No developer or manager will get promotions for it.

- The actual management of the companies will not promote or compensate engineering managers or developers for maintenance projects since it doesn't contribute to "line goes up"-economics.