Depends on what you all count as a "phase of boredom"
I think I never really had such a phase (or that it lasted longer then 2 or 3 weeks).
My first thought here was: "How can this be that people who are here for only 1 or 2 years are bored with LFS?"
As I never really stopped playing it for more then a few weeks in the last 4 and a half years.
Sure sometimes I only race on 3 or 5 days/per month and usually I have the most fun with it when racing in leagues
but I never really stopped playing it at all or never stopped playing it for longer then a few weeks.
But then I had other reasons or things to do that hindered me (moving, new job, holidays etc.)
Back to my first thought:
Maybe one reasons for newer people is that there are not that often major updates
like we had in the past or early years of LFS.
When I started there was only the demo available, (At first I didn't liked it that much tbh)
Then several updates later I really started to like LFS
We had only 4 tracks and 6 or 7 cars
Then I think the MRT came as an X-mas present, then I played the demo for several more months,
then S1 came out, I played the demo for some more months as I had no DSL during that time
Then I finally bought S1, then S2 and during that till today there came so much new stuff and lots of big updates:
"Old and new LFS World, Skid marks, from iirc 10 players per race to 15 to 20 up to 32, the CMX Viewer,
Westhil, Aston, an own LFS Forum (instead of the slow RSC we only had), FBM, Clutch pack, flags, tyre heating,
BMW F1, auto patches, engine sounds, outgauge stuff, refurbished BLackwood,
replay hotlap analyzer and lots and lots of more "smaller" stuff".
Over the years I really got used to the "It's ready when it's ready" mentality.
Because whenever something new came out for LFS it was great and well thought or tested.
So I'm used to wait for good things.
Another reason for not stopping is for me of course my Team.
There is always something to do, something to talk about, something to plan or to test
and I never really get bored.
But that's me, I have no patent remedy for others.
Playing other games for a few weeks is for sure a good thing
and if you got no fun driving LFS, don't force yourself to drive.
Testing other so called racing sims is for sure also a good idea
because when you then go back to play LFS you know what makes it special
and I always got back the fun instantly