It's not just about rain and mud. It can, I've seen places looking like a swimming pool (10 m long, as wide as the trail, up to 30-40 cm deep). No fun.
Then, it's about available time too. With 2 young kids it can be handy to get an indoor ride in the evening, when I can't leave them alone at home. Sometimes, specifically in the winter, it's too dark outside apart from lunch rides. Weekends are busy!
Looking at cost, here is my rough estimation:
- A basic but still good quality Home Trainer: 200€
- Accessories (floor mat, front wheel stand, fan, etc...): 50€
- Rear tire (in case you don't have a road type tire): 20€
- Sensors (Speed, cadence. You need it unless you invest in an expensive home trainer): 60€
That's already 330€.
Then, TrainerRoad is 12€/month, Zwift is 10€/month. That's about 50€/year as you don't need it all through the year.
I own an elliptical indoor "bike" (which is not a bike). Using it last winter, I've seen a lot of benefit but this is closer to running then cycling. I can see how a Home Trainer could help me to be in shape 2 month earlier and then enjoy a longer period on the bike as soon as the weather is getting better.
Sounds nice, sounds like a new money hole indeed