The number one thing that needs to be improved, which was not covered in the poll, is time. It takes more than two full calendar years real life time to train a player up from age 18 into a fully developed talent. This is the most unattractive aspect of the game.
First of all, this is a ridiculous amount of time to expect anyone just joining the game to commit to
Secondly, should you actually accomplish this, you don't have time to train a second set fully before the first set starts skill deterioration. Basically, it isn't even possible to train a complete roster in house and be competitive. Currently, you can train a set then you are forced to dip into the TL to put a team around your homegrown players.
I really think training speed needs to be cut in half. In real life, most players are nearly fully developed by age 22 or 23. If BB matched that it would be actually attractive to build your own team. Teams that have made it to the top, have almost zero interest in a full rebuild under current structure. It should be possible to build your own team through the draft and development and not required to rely on free agency in order to compete. Easily the biggest road block in managers staying long term.
Cut training time directly in half and watch the interest in the game grow.