You can rollover to get around contribution limits [1], and the government gets your money now rather than later,

> A Roth IRA rollover (or conversion) shifts money from a traditional IRA or 401(k) into a Roth. You can get around Roth IRA income limits by doing a rollover. You'll owe tax on any amount you convert, and it could be substantial.

Limiting the max amount would reduce near-term government tax revenue. So I don't think it would happen.

[1] https://www.investopedia.com/how-to-do-a-rothira-rollover-47....