They can be made from different materials. Common ones are briar, olive, or fruit trees, but also clay or corn cob... Basically anything hard enough to withstand the burning leaf and low in tannins, which are harmful to smoke.

The shapes (and finishes) are mostly about look and feel, but as another commenter mentioned, the stem length affects temperature. Hot smoke (like a hot drink) results in tongue bite, but puffing gently and not smoking like 10 bowls back-to-back makes it easier to avoid.

There's also a wide variety of different leaves, preparation methods, and toppings to explore, and their properties can change depending how you store / treat them. The different materials influence the flavor a bit, too. Most pipe smokers have multiple pipes and rotate them to avoid mixing aromatics with non-aromatics or latakia (la-TAK-ia).

It's not expensive or difficult to try. If you know anyone who's interested, just find a cheap pipe (maybe something with 9mm filter), pick a tobacco that looks good, and watch a 5-minute video about how to pack and light the bowl. Then enjoy together with a good beverage. If it's enjoyable, watch another video about cleaning the pipe, and take it from there.

Some people smoke multiple times a day, and others smoke less often. It's not like pulling a cigarette out of the box, though, and the mild 'inconvenience' of packing and cleaning helps to not chain-smoke. I prefer the process, don't mind waiting for a good thing... not in a hurry.

I've also read what I could find about health risks. Pipes are lower risk than cigarettes, hookahs, and smokeless tobacco (of which the loose variety is riskier than pouches). They're a bit safer than cigars due to volume. Newer studies show vaping is also riskier than pipes, depending mostly on the liquid. Tobacco-free nicotine pouches seem to be the safest, but more research is needed. I'm not an authority, though, so #doYourOwnResearch, and definitely reply if you see any info that needs to be corrected in this comment.

The longer the stem is (the piece between the bowl and your mouth), the more time the smoke has to cool down before it hits your mouth, and some believe this gives a better smoking experience.

The big advantage is you can fill a pipe with whatever you want. Smoke shops at least used to have a large selection of smells and styles - think like a modern coffee aisle

Maybe that functional space is taken over by vapes these days

I think it’s “smoother” but I’ve never smoked one so I cannot confirm