Sage has a wide range of solvers available to solve MILp. However, all these functionalities require that the problem is to be implemented following Sage's API.
In contrast, Gurobi allows to solve MILP problems, directly reading from an LP file. This comes in handy, as there's no need to follows Sage API.
It seems that, Sage does not yet support directly reading LP files. It will be helpful if someone can comment specifically if such functionality is available or will be implemented in near future/a ticket can be initiated.