That's a great question as well.
Most nations don't have very restrictive statutory rebuttable presumptions on mergers. We're aware of Germany, which codifies 40% as the cut-off point for rebuttable presumptions on mergers.
It's really important to be able to continue to monitor the market and understand how things are evolving. There are situations, for example, where a large, dominant player might have 50%-plus market share, and two smaller competitors wish to merge to bring them just over the threshold of 30%. That would represent, in some cases, a positive for competition and a positive for consumers.
To codify it into law and then make it very challenging to modify a certain threshold could have some unintended effects on businesses, and on the economy and the markets as a whole.