Quick Question. Why are row mappings in their own underscore table?

mysql> show tables;
+---------------------------------------+
| Tables_in_default@default             |
+---------------------------------------+
| CheckedOutDataRow                     |
| DataRow                               |
| Dataset                               |
| Function                              |
| FunctionRun                           |
| Label                                 |
| LabelReservation                      |
| LabelingFrontend                      |
| LabelingFrontendOptions               |
| Organization                          |
| OrganizationInvite                    |
| Permission                            |
| Post                                  |
| Project                               |
| Task                                  |
| Team                                  |
| Type                                  |
| User                                  |
| _AgreementFunction                    |
| _AssignedFunctionRun                  |
| _CheckedOutRows                       |
| _CreatedDataRow                       |
| _CreatedDatasets                      |
| _CreatedFrontends                     |
| _CreatedFunctions                     |
| _CreatedInvites                       |
| _CreatedLabels                        |
| _CreatedProjects                      |
| _CreatedTasks                         |
| _CreatedTeams                         |
| _DataInDataset                        |
| _DataRowLabels                        |
| _FunctionRuns                         |
| _LabelReservations                    |
| _LabelType                            |
| _LabelingFrontendCustomizationOptions |
| _OrganizationCheckedOutDataRows       |
| _OrganizationDataRows                 |
| _OrganizationDatasets                 |
| _OrganizationFunctionRuns             |
| _OrganizationInvites                  |
| _OrganizationLabelReservations        |
| _OrganizationLabelingFrontends        |
| _OrganizationLabelingFrontendsOptions |
| _OrganizationLabels                   |
| _OrganizationPermissions              |
| _OrganizationProjects                 |
| _OrganizationTeams                    |
| _OrganizationTypes                    |
| _OrganizationUsers                    |
| _ProjectCheckedOutDataRows            |
| _ProjectDatasets                      |
| _ProjectLabelReservations             |
| _ProjectLabelingFrontend              |
| _ProjectLabelingFrontendOptions       |
| _ProjectLabels                        |
| _RanFunctions                         |
| _RelayId                              |
| _SkippedRows                          |
| _Tasks                                |
| _TeamMember                           |
| _UserCheckedOutDataRows               |
| _UserLabelReservations                |
| _WhitlistedProjects                   |
+---------------------------------------+
64 rows in set (0.00 sec)

mysql> select * from _OrganizationUsers limit 1;
+---------------------------+---------------------------+---------------------------+
| id                        | A                         | B                         |
+---------------------------+---------------------------+---------------------------+
| cjgv79dicfh9i0876b5c2w0ts | cjccycyq6hpje0134aktmtshq | cjccyczdih7lb0161ujq9q1ml |
+---------------------------+---------------------------+---------------------------+
1 row in set (0.00 sec)

I'm wondering the same thing. Maybe you'll get more response on the forum: https://www.graph.cool/forum/