Why is the Bode Plot start frequency minimum 10 Hz?

The minimum start frequency is set to 10 Hz because of the extended acquisition time required to collect enough data to ensure a useful level of measurement accuracy. If the low limit was 1 Hz, the scope would need to test 10 cycles (to maintain specified accuracy), so the time base will be 10 s/div. This would make for a very slow test.

Other issues: For low frequencies/long acquisitions, the cabling/etc can be easily disturbed, causing the scope to re-acquire. So we limit it to 10 Hz.