Solution : https://service.sap.com/sap/support/notes/132424 (SAP Service marketplace login required)
Key words : 
multi-table tablespaces isolate, dedicated single-table tablespaces, db2 v7 reason, db2 optimizer chooses, optimal access path, older db2 releases, avoid regularly repeating, systables      set cardf=-1, systabstats      set card=-1, sysindexes       set clusterratio=100
Related Notes : 
       
| 765983 | DB2/zOS: Reducing number of DSNACCOR REORG recommendations | 
| 712019 | |
| 711245 | DB2/390: Catalog modifications | 
| 507824 | DB2/390 V7: Real Time Statistics and DSNACCOR | 
| 330059 | |
| 192320 | DB2/390: Ensuring index access for volatile tables | 
| 181286 | DB2/390: Excluding tablespaces from RUNSTATS | 
| 116698 | DB2/390: Optimizing Access to Tables VBHDR, VBMOD, VBDATA | 
| 113008 | DB2/390: Maintaining Catalog Statistics | 
| 82072 | DB2/390: Invalidating Cached Statements |