Users of such teams are classified as non-serious users. Hence, they are unlikely to spend money and/or complete offers as compared to the other type of user that are likely to be put in 5-7 stars league. So, on the business side of view it is better to put the non-serious users together, and put the serious users together. If serious and non-serious users are put together, serious users will feel less need to improve their team significantly as compared to when they have been put in a mostly serious-user league. The higher the level and the tougher a competition is, the more there is the need for a serious user to improve his team as advantages in quality will likely be very significant in such cases for deciding the top 4 and top 6. Why can't you see that?
'playing the game for two years and having the mongul 1 achvm ? bought only 30 players from the beginning of the game' Such users are probably non-serious users. So, it is better to group them together as they will not likely contribute directly or indirectly to the revenue of the company for the case of the league (for example, directly: buy tokens; indirectly: cause other users to buy tokens). But, they may contribute indirectly for the case of the Cup.
Why the selection is done based on quality? Consider the denotation P(X) to be the probability of the event X to occur. For a particular level, P(a team is managed by a serious user) is significantly greater than P(a team is managed by a non-serious user) when the team's average quality relative to its level is greater. The P(serious user to spend money or complete offers) is greater than the P(non-serious user to spend money or complete offers). This is an example of how statistics are used to make business decisions.
A similar approach can be used for the Cup.
P(the lower level team is managed by the serious a user) is greater than the P(the higher level team is managed by a serious user). Hence, P(serious user from the lower level will spend or complete offers) has been increased as he has been put to compete against higher level teams.
These probabilities are well respected for the lower-mid, mid and mid-higher levels. Hence, this concern the majority of active serious users - the major fraction of users that are expected to contribute significantly to the revenue of the company. The probabilities are likely not be well-respected at the extremes (very lower levels, for example level 1 and 2, and very high levels, for example 30+).
Very few serious users use the method of tanking and/or draw fooling in this game. You have seen it based on how you play the game. See it on the serious-user, token buyer or non-tanker side of the game. See it as a businessman. It is clear that the change in how the league draws are done was a business move.