Why not though? You accrue more ranking points in tennis and golf by winning a major instead of an ATP/ PGA regular event.
They're completely different systems. Tennis ranking points are given in fixed amounts by quality of tournament, i.e. 250 points for winning 250 series, 1000 points for winning a grand slam. A grand slam has better players than the 250 series so you get more points for winning it.
Cricket rankings have pretty much nothing in common, most likely because it's a team sport compared to individual. Points are dynamically calculated based on the relative quality difference of the two teams playing each other.
There is no statistical reason to give greater weighting to and Australia vs India World Cup ODI than the same match-up as part of a standard series. It's the same teams, the odds don't magically change from 70-30 to 20-80.
Yes, the rankings are a much better indicator of quality than the World Cup result. Rankings are a medium-term average played over different sets of conditions. World Cups are a much smaller sample, and are inevitably going to throw up biases that favour certain teams.
Of course, a World Cup is much more important than some mathematically calculated index that has little public connection. But it wouldn't make the slightest bit of sense to add weighting to a World Cup match. Again, grand slams give more points than lower series because they contain greater quality - something already taken into account in every match calculation with the cricket rankings.
Essentially, World Cup games are the prestige. They're what actually
matter. The ICC rankings are there to provide an unbiased, medium-term, large-sampled snapshot of the most consistent winners in cricket.
