If free loading and performance are the issue then why stop only on Zimbabwe? After all, we do have plenty of freeloaders and non performing actors in test status list.
Test format is depleting already and we only have very few teams that can match or even capable of playing 5 long days and still makes it interesting. That is one of the reason England is doing something called bazball even if it is not giving them the results they wanted while other teams like AUS and IND makes it aggressive also a balanced approach.
If we only keep these best teams and remove others then the potential viewers will reduce that affects the revenue and ultimately every sport is a business so they will try to keep it stretch as long as possible while concentrating on the profit making format that is why T20 is given more importance than others.