[drc]

There are a lot more baseball card collectors out there than baseball ticket or First Day of Issue envelope collectors, so if something is considered to be a baseball card there will be more demand and be financially worth more.

That's the financial answer to why whether or not something is a baseball card is important. I'm not at all saying financial value is the only way, or the best way, to consider or justify or measure a piece of memorabilia.

P.s. I don't believe anyone knows what is the first baseball card. In the area of early cards there is a lot of gray area, unanswerable questions and missing information, differing definitions and points of view and we're not certain when some cards were made. For two given early cards, the hobby may not know which one was made first.