I've long suspected that these "megacorporations" are nurtured for national security reasons, to consolidate and project power. The disproportionate influence is by design, a feature not a flaw. Especially since those who make the rules are owned by such powers themselves, including those responsible for intelligence (corporate spying, undermining workers unions) and regulation (not preventing Metalphabetamazons from dominating a wide range of industries).
This has at times been explicit policy. It's a big part of how Japan (re-)joined the developed world so fast after WWII—they gave a few megacorporations a captive home market to keep them healthy & safe, used incentives to get them to pool R&D money and share the output, then set them loose on foreign markets.
