In battletech, tanks are still very much used and useful. It's a pros and cons thing.
Pros
>Comparatively cheap (This is the main reason)
>Smaller/low profile
>Easier to operate
>Cant fall down
>Little/no heat worries
Cons
>Much less maneuverable
>Slower
>Easier to kill
>Less weapons/adapability
Also remember that BT has a non-real tech called Myomer Fiber that are pretty much hyper efficient synthetic muscle and is entirely responsible for battlemechs being viable.