Answer:
Usually this is because the logic runs in the Syntax Check mode which is used to validate the logic when editing/saving. The limit was brought here not to slow down the saving when all you want to do is to check that your code 'compiles'.
But running a logic in the Syntax Check mode also serves another purpose: to find the input parameters (to populate api.option(s)) before running the logic in the normal mode. For this reason the limit will be increased from 1 to 200 result rows in Vesper 6.0 (configurable per instance). There are also dedicated inputs for PA, like api.datamartFilterBuilderUserEntry() and api.getDatamartContext().dimFilterEntry() which are not affected by any row limits.