One of the columns in VOMA (Vertical Online Market Analysis) is market share - it indicates how important the keyword is to the market represented by the parent theme. It's not an indication of relevance between the two keywords.
If the parent theme has a large number of competing pages and the keyword has a very small number of competing pages, there is no way that the keyword is highly important to the parent theme.
However, it might still be highly relevant to the parent theme.
Let's look at mountain climbing, for example. There could be an obscure piece of equipment that is used in mountain climbing, we'll call it a widget. A lot of mountain climbing can happen without a widget, but when ever you use a widget, it's always because you are climbing a mountain.
So the widget is highly relevant to mountain climbing, and mountain climbing is highly relevant to widgets, but widgets are not terribly important to mountain climbing because most mountain climbing does not involve widgets. So when you drill into mountain climbing, you'll find the co-occurrence of widgets is pretty small.
Let's take a specific example.
I just did a drill on 'first time home buyer' - needless to say 'home buyer' is 100% important to the parent theme - you're not going to have a 'first time home buyer' conversation without talking about a home buyer. 'Homes', however are only 65% important because sometimes you talk about 'first time home buyers' but you aren't talking about the homes they are looking to buy - maybe you are focused on home loans or grants or programs for first time buyers, etc. In fact, obviously you are talking about something other than homes 35% of the time.
'Home inspections' are also key to buying a house, but they only have a 9.35% importance to the 'first time home buyer' niche. That means right around 10% of the conversations involving first time home buyer include the idea of home inspections.
Market share is not represented in Krakken as an exclusive idea. If you total up all the market share represented in a drill you will get a lot more than 100%. This is because most conversations cover more than one topic.
For example, it's possible that in the 'first time home buyer' niche there will be conversations that will talk about both 'homes' and 'home inspections'. Therefore, it is an incorrect assumption to think that these two terms together cover a total of 74.35% of the first time home buyer market.