There are several valid use cases on which adding large content for the reason parameter associated with a nodeLostService event is justified. An example is using HttpPostMonitor to retrieve the status of several elements through a SOAP interface, or doing something similar through the BsfMonitor; and then explain in detail why the the service is not running when creating an outage.
There is a physical limitation to 255 characters inside the PollStatus class. It seems like this limitation is associated with a table on the database called location_specific_status_changes that is not being used (verified on Meridian 2016 and Horizon 20.0.1).
Either way, there is no reason for limiting this field considering that the events.eventparms column is already defined as text, and the table that is enforcing this limitation is not even used.
I suggest to remove this limitation from the code and the database.