Why do so many recipes use chillies?

I think that fresh chillies, de-seeded & finely chopped provide a really good background flavour that doesn't overwhelm the food. So that is my response to the "wondering" as I use them a lot. I probably wouldn't use them with lemon sole, but do use them with fish and with other things as complementary rather than "overpowering" flavours.
You don't say why you can't eat them - if it's about flavour or "hotness" then I would use peppers and/or paprika, but if it's about a reaction to them, I don't know if those substitutes would cause the same problems.
Chillies come in a lot of degrees - you can get charts but I find them confusing, so I cut a piece and taste it to decide how much & how to use it.

Why do so many recipes use chillies - because idiots like me grow a few plants, then are over run with chillies and need to find something to do with them. We have them fresh, dried, pickled, crushed and anything else we could find to do with them. Does this idiot learn - no!!! I have another six plants this year!!

I can't eat chillies at all, they make me ill as does black pepper. It has taken years of watching what I am eating to reach this conclusion. Thirty minutes after ingesting the infernal stuff I get a sore stomach and nausea and it seems to be the entire length of the digestive tract, sometimes i'm not aware of chilli in the food until the symptoms start so it must be even the smallest trace. So many people have told me that I can't be reacting to chilli and pepper and it must be the cream or the alcohol or some other ingredient. I have found it is the outer husk of the black pepper that is the problem, I can eat white pepper in cooked dishes with no problem. Takes me ages to shop if I want to buy pre-prepared sauces etc.

I got used to eating small amounts of chilli when I lived in Thailand, though the Thais used to laugh at my small amounts. When I came back to Britian I stopped eating chillies. Thai food here is nothing like Thai food in Thailand; the seafood I was eating was just about straight out of the sea, and fruits and vegetables were equally fresh. However, on a recent visit to DD1 she showed me how she makes curry and I've tried her method since, with help from Nigel Slater's attitude to food and am quite liking a bit of chilli occasionally again. My husband is a chilli fiend so he's pleased but actually he loved a curry I made with other spices but no chilli. So did I so we'll be having that one again, especially as it uses my favourite spices: coriander seed, cumin seed and cardamom seed.
harrigran, peppers have a noticeable effect on my digestive system too but because I take a lot of codeine for arthritis, it's quite a useful effect!

Chillies are a useful spice that complements other strong flavours. You can reduce the hotness by scraping out the seeds. It's not the seeds that are hot but the membranes surrounding them, but scraping out the seeds scrapes out the membranes too. Sole is a lovely delicate fish and not the partner for chilli; monkfish, on the other hand, is quite"meaty" and robust and you can use chillies without disguising the flavour of the fish. If you don't want the chillies in a recipe, leave them out – it's unlikely to make much of a difference in a carefully written aromatic dish; you just lose the heat.

Philoheart, I am in your corner on chillies.
My taste buds can spot a chillie at 100 yards!! Bring on the yoghurt!