I don't know why you wouldn't be able to clone tomatoes, but then again I never tried. You can clone tons of other plants, some a lot easier than others. African violets are not that hard but they take a long time to root and produce a new plant. Cactus are usually easy clone. Generally clones come from perennial plants as opposed to annuals. Cannabis is the only annual I can think of that is propagated by cuttings. If you want to start with something easy, try some kind of vine houseplant like English ivy. Sweet potatoes are easy to start as cuttings, if you can get one of the tubers to root in water. Cut off a few of the vines that sprout and plant them elsewhere, very easy.
A few comments here.
The easiest plant to clone I've ever seen is mint. Its basically a water-loving weed that easily puts out roots and grows fast. One time I had a nice meal at a Thai restaurant, and they garnished my plate with a sprig of mint. For the hell of it, I literally took that sprig off my plate, brought it home and rooted it successfully just by dropping it in a cup of water for a week.
Tomatoes are actually fairly easy to clone, should you care to try.
The reason most people don't clone annuals is because they're generally crop plants that are easily grown from cheap ceed. Sure, you CAN clone a tomato, but the ceeds are only a few cents and readily available, so there is little reason to try.
Drug cannabis is a specific exception here for a number of reasons, mostly having do with the way the plant is grown.
First of all, only female plants are generally desirable, the plants are typically grown seedlessly, and the legal status of the plant means that ceeds from drug strains are typically both expensive and somewhat hard to acquire. If you look at HEMP cannabis strains. . .nobody is growing those from cuttings; everyone starts from ceeds.
The next issue is specific to the technique of indoor cultivation, where people want the most rapid consistent turnover possible, and from a technical standpoint its simply faster to "crop" cannabis when starting from cuttings since unlike seedlings, cuttings are sexually mature and can be put right into flowering.
Lastly, many "strains" of cannabis are actually hybrid plants, where ceeds simply are not available and/or cannot even be created.
Although these plants actually are fertile, somewhat like seedless plants (that can ONLY be reproduced via cuttings), in practice the only way to get true genetic copies for repeated cropping or propagation is via cuttings.
