Facebook's payments to use the Signal protocol pay the bills. Same reason why Moxie was fine with Google disabling E2E by default so they could use chat for ad

Facebook's payments to use the Signal protocol pay the bills. Same reason why Moxie was fine with Google disabling E2E by default so they could use chat for ad targeting, after attacking other software for doing this, and with them tying enabling it to inconvenient behaviour like disabling the chat log that discourages all but the most paranoid from using it.