The reason they're treating De Gea this way is because he has no pride, they have seen him for whom he is, they know he is welling to play for the club no matter what. If he has that spirit of forcing his way out from the club by now they won't waste time to double his salary from the beginning even if he'll be the second choice. Like who won't want a goalie like De Gea to be on his team? That's the thing with Manchester United and if you check no club is even coming for those players they're ready to sell, see how bad it is for UTD, they can't get any business done as it is.
I'm sure this is a step that Manchester United will regret in the future, De Gea is a goalkeeper who has very good quality and even last season he made many brilliant saves to keep Manchester United's goal but he was completely thrown away like without a price self.
Now De Gea is being linked with a Saudi Arabian team that dares to pay him a very high salary, I think it will be a good choice for De Gea while closing his football career, now De Dea is 32 and maybe he still has a few more years to be consistently in good performance.