This was a decision that was made to improve the turnaround time of scans for all of our MSP partners based on the typical size of the companies that are serviced by them.
We originally had a larger IP limit and found that people were indiscriminately running large ranges where no IP's were even in use - and in many cases not even belonging to the company for which the scans/assessments were intended.
Of course there are certainly legitimate cases where larger scans are needed. For those cases, the scans will need to be broken into multiple scans and reports.
Please do not schedule scans against IP ranges that do not belong to your customer. Also, please avoid scanning IP addresses that are not active. Scanning an inactive IP address actually takes significantly longer than scanning one that is in use.