This database was built using data from BEFORE Google required active ad accounts to get good keyword data & before they started blending data together for similar terms. Even if you set up an AdWords account and spend significant sums of money with them, they may require you to run your ad campaign for 3 or 4 months straight before they will show reasonably precise data instead of exceptionally broad data ranges.
Google prefers to not share long tail searches in this tool – because the tool is designed for Google Adwords advertisers. If advertisers bid on those long tails – they would have less competition and therefore pay less for the Adword, and therefore Google would make less money e.g. bidding on the term weight loss for girls under 18 is cheaper than weight loss.
Basically, Google shows the autocomplete suggestions whenever you start typing anything into Google search box. It is in Google's best interest to show the most relevant keywords in the autocomplete suggestions. Keywords that would help Google to retrieve the most relevant websites and help users find the most relevant content for their search query.
I ditto what you are saying. All of the keyword volume data the system is stating is completely way off, false and misleading. They are pulling these numbers now from 3rd party sources, which we all know are directional, but in many cases in left field! I just signed up and will probably be cancelling because I can’t trust or rely on their data. What a shame, because before it was such a great tool.