1. The £12,500 promise is for this parliament, i.e. before 2020. It's probable that they will exceed the promise, but not in July.
2. Increasing the personal allowance no longer makes much difference to the poor and underemployed: the disadvantaged in society. Thanks to the last parliament, they are out of this category.
Increasing the benefit is now primarily a small tax benefit for the working middle classes that has the significant advantage of appearing to be progressive.
Shortly to increase to £12,500 in George Osborne's next budget in July.