Hello,
This is because the TPP1000 does not use the 1MOhm path, instead it uses a 250kOhm termination. The termination resistance is also automatically set by the scope when you connect the probe. For more details about this 250kOhm path see the following FAQ:
Why isn’t the TPP1000 (Tektronix Passive Probe 1GHz) compatible with my scope? | Tektronix