L298n speed control not working

Why not?


            +---|EXT|--------|USB|---+
            |    PWR          A5/SCL |
            |                 A4/SDA |
            |          UNO      AREF |
            |                    GND |            +-----+
            | IOREF          SCK/D13 |            |SERVO|       
            | RST             DI/D12 |            | GND |-------+
            | 3V3             DO/D11~|----+       | VCC |-----+ |
      +-----| +5V                D10~|  +-|-------| SIG |     | |
      |     | GND                 D9~|--+ |       +-----+     | |
    +-|-----| GND                 D8 |--+ |   +------------+  | |
  +-|-|-----| Vin                 D7 |  | +---| ENB  L298N |  | |
  | | |     |                     D6~|--|-----| ENA        |  | |
  | | |     | A0                  D5~|--|-----| IN1     5V |--+ |
  | | |     | A1                  D4 |--|-----| IN2    GND |--|-+
  | | |     | A2             INT1/D3 |--|-----| IN4        |  | |
  | | |     | A3             INT0/D2~|--|-----| IN3        |  | |
  | | | +---| A4/DA  RS CK DI  TX>D1 |  |     +------------+  | |
  | | | | +-| A5/CL  GD D0 5V  RX<D0 |  |     +------------+  | |
  | | | | | +------------------------+  +-----| SIG  FLAME |  | |
  | +-|-|-|-----------------------------------| GND SENSOR |  | |
  | | +-|-|-----------------------------------| VCC        |  | |
  | |   | |  +---------+                      +------------+  | |
  +-|---|-|--| 9V  PDB |                                      | |
    +---|-|--| GND     |                      +------------+  | |
        | |  +---------+                      |  MLX90614  |  | |
        | +-----------------------------------| SCL    VCC |--+ |
        +-------------------------------------| SDA    GND |----+
                                              +------------+