A harder question to answer may be why not. With so many choices, tea cup collecting can satisfy any pack rat's urge. They are pretty, plentiful and can be had even if you're on a tight budget. Go to any garage sale and you are likely to find at least one set for sale and the thrift stores usually have a selection of tea cups and saucers on the shelves. Add Ebay and shops (both online and brick and mortar) to the mix and you will probably never know the frustration of not being able to find that new piece to add to your collection. From whimsical to elegant bone china, the choices are limitless.
And how can you get bored with them? I had a customer once that bought several sets for a bridal shower. You would think a gathering of that sort would require an elegant matching set for her guests. But her idea was so much more fun. She wanted each place setting to have a completely different tea cup and saucer, no repeats. Think of how much fun any tea cup collector at that party would have had looking at the pretties! It would be even easier to do this on a smaller scale with a close knit group of friends over for afternoon tea.
Cups and saucers can take up just one shelf in your china cabinet or take it over completely. You can fill your walls with shelves of them and never have 2 sets alike if that's your fancy. You may have identical shapes, but the number of decorations are endless. That being said I would guess that once you start collecting tea cups and saucers, you might very easily expand your collection to include tea pots, sugars and creamers and even tea and dessert sets. It would be hard to resist ;)