For the person selling a domain name to you, there may be many reasons to do so. For a domainer (i.e. somebody buying and selling existing domain names), it is an investment. But many domainers do not limit themselves to buying names and selling them at a profit: a number of them develop Web-based projects, but they do not have enough time for all of them. Moreover, they take risks: they buy domain names (often hundreds or thousands over the years), they pay for them prices that are not always cheap, then they need to pay yearly renewal fees for hundred or thousands of domain names, without any certainty to sell them finally – one domain name is sold, while dozens other domain names remain unsold.
If you take all those factors into account, it will become obvious that (serious and honest) domainers are just investors like any others. Moreover, thanks to them and to their foresight, you may find that very domain name of interest to you: if it would have been bought by a competitor, it is very unlikely you could get it some day. This way, your perception of domainers will probably become more positive and realistic.
Although the comparison has its limitations, like any comparison, we could compare domain names with real estate. Some properties don’t become more valuable over the years – or their value even decreases, and finally they must be sold a t a bargain price. Other properties at top locations gain more value year after year. Everybody who has travelled to various areas of the world over the past 30 years has probably had opportunities to witness cases of pieces of land or houses of which the price has multiplied by 100% or 1,000% in a matter of a few years, due to changing circumstances. Should their owner still sell them at their original value? Nobody would dare to suggest it! Domain names are very similar to such developments in real estate.