The answer to your question is pretty much simple: because they hold little to no real-world value at all. They are just a by-product of hype with no significant use cases.

I strongly advice you to conduct extensive research first before venturing into any investments. It is critical to analyze the project's road map and white paper. Educate yourself with its fundamentals and its developer's background. An active and positive community that supports the project is noteworthy too. Numerous altcoins I can recommend which best suit the qualification above includes ETH, ADA, LTC, BNB, and this promising gem XSN.