Correction: 2020 Proposition 22 was an initiative statute that modified the Business and Professions Code (https://leginfo.legislature.ca.gov/faces/codes_displayexpand...), not the California Constitution. And the clause that allowed amendments with 7/8 supermajority exists to make it easier to amend than if the clause did not exist, since by default initiatives can’t be modified by the legislature at all (Constitution Article II Sec 10(c) https://leginfo.legislature.ca.gov/faces/codes_displaySectio...)! It is common to choose a threshold above the known opposition (my earlier comment with more examples https://news.ycombinator.com/item?id=28259306), and 7/8 is above the 73% that voted for AB5 (https://leginfo.legislature.ca.gov/faces/billVotesClient.xht...).