FWIW, HMH requires taking HM down for several weeks in Sept to install it and then several weeks in Jan to remove it. Apparently WDW has been reluctant to do this because so many visitors come from out of town and they do not want to take a major attraction like HM down so regularly every year. It is more likely to upset their visitors who come less regularly.
At DLR, a much higher percentage of visitors are locals who are largely regular visitors and day trippers, and the impact is much less. So DLR feels more latitude to do this.