Plenty of reasons. Most banks won't give bank accounts to Bitcoin businesses let alone loans. Individuals might not have access to VC or angel investor types.
I assure you cryptx' CEO does, and the bitcoin related businesses that actually have a sensible business plan (and capable management) dont seem to have any problem securing VC capital. I sure wish I could have bought shares in Bit-pay when it launched and would still very much like to invest today, but they didnt need an unregulated BTC IPO to get their funds.
There's nothing inherently wrong with fundraising in this way (or similar initiatives - crowdfunding, etc), ignoring the obvious (i.e. securities laws).
I agree, there are cases where it makes sense, like AM, but just asking yourself the question will in the vast majority of current bitcoin related securities reveal it does not make sense. For instance, if bitcoin-trader pays out 3000% interest per year on fiat and BTC deposits alike, allegedly by "margin trading", it doesnt pass the sniff test of why they would need (ever more) external capital.
Unfortunately, scams are scams and BTC-TC and Bitfunder shutting down hit the BTC unregulated securities markets hard.
Pretty much none of the securities trading on either exchange were worth anything anyway. Closing down only exposed faster how worthless these things were.