Many factors.
It's all about scale. Big companies play by different rules. Some of these companies can be very influential and can negotiate directly with the government in some cases.
Once you reach a certain size, having proper substance in Bermuda, BVI, or wherever it may be is just a rounding error compared to saving millions in taxes.
These companies are also so big that they can easily take a tax authority to court and keep escalating, whereas most individuals and SMEs would rather pay up than fight. For the tax authority, this means they have to have a much stronger case against a large enterprise.