Why can't Historical data and Analyze All be switched on simultaneously?

If you want to import keywords and analyze them with the freshest SERP data, switch off the "Historical data" switch. It will analyze all your keywords without checking if any was analyzed in a previous report.

If you want to import keywords but want to check first which ones have been analyzed in one of your previous reports, switch off the "Analyze All" switch (and keep the "Historical data" on).

Then, once inside the report, you can decide which keywords you want to analyze.