It only takes a handful of extremely passionate engineers > It only takes a handful of paid engineers, full time assigned to the task
What I mean to say is that with a monorepo, you leave the door open to essentially passion-driven contributions made by the other half of that 2%. In non-monorepo environments, the barrier to uniform adoption is too high for someone that isn't full-time assigned to the task to justify.
Some people are genuinely passionate about this stuff, and want to take on the task of migrating the entire code base, because it's a fun challenge and it'll improve their day-to-day work every day for the remainder of their employment. They're very rare, but they do exist, and with a monorepo those people are better-equipped to drag the company forward.
I have some news - passion is not enough, and there are more than 2% of people working on things they are passionate about - it only 2% get lucky.
I can think of a few instances in my recent career at large monorepo company where I have built something on the scale of "passionate, could improve our working lives"
One died because ... well I gave up, two are used locally by my team and those I could persuade, whilst other solutions built by others for the same fix have gone on to be blessed officially, (ie replaced by grassroots competition) and one was replaced by a fully mandated and funded project that spotted the need and just steamrollered over all the local fixes.
One is still outstanding and I think well worth pushing still.
But I don't dream of the big win where suddenly the Board says "why, without your glasses Miss Moneypenny you look ravishing".
I get paid, I work, and I try and make the world a bit better where I can. I am passionate about it. But i don't write blog posts about how passionate I am.
Maybe I should :-)
It only takes a handful of extremely passionate engineers (and I really mean a handful, like less that 2% of engineers in an org) to raise the quality-floor of the entire codebase.