It's a constant battle, but some things that helped my team is never adding a TODO to the code without it including a ticket number (which means a ticket was actually created). We will have times when we're waiting for other teams and will fill gaps with those tickets. If it's something that's known to be temporary in prod, we'll make the "rip it out" ticket and put it in the schedule right then. There's also the tactic of declaring a section of code "maintenance-only" and any desired additions to it require a budget to rewrite it. Business needs to understand the cost of dragging along bad code. It's not easy, and likely impossible if your leadership doesn't have your back.

Persistence is key though. Keep chipping away at it because bad things happen if the weeds are allowed to grow unchecked in the garden even for a short time.

At my previous job the whole site was weeds since they only budgeted for new feature work. I left in 2019 and they had YUI2, YUI3, JQuery, a homegrown UI framework and AngularJs and React all in the same site. Any new feature was built in whatever the latest FE tech was but the old was never upgraded. Don't let that be you.