Just because the crowdfunders don’t seem to register doesn’t mean that they are not supposed to.  But you have to differentiate among the types of requests being made on these websites.

Charitable solicitation registration is required when an individual or an organization seeks to raise funds for a charitable purpose or with a “charitable appeal.”  Individuals asking for funds to create a music album of their own music, or producing their own movie for sale don’t seem to be invoking a charitable appeal because there is nothing charitable about their work.  (They might have to worry about securities regulation, but most of their supporters get a free album or a ticket to the film, not an investment interest in the business.)

If a charitable organization were to ask for funds to make an educational film, or if an individual sought money to take underprivileged kids to the circus, those would be charitable appeals.  Individuals (even if not organized as charities) or organizations asking for contributions for charitable activities or with a charitable appeal would normally have register to solicit in the 39 states and the District of Columbia that have charitable registration statutes unless specifically excluded or exempted from registration.  They would have to register as charitable organizations because they are soliciting for themselves, and not as professional solicitors who ask for others.

But the charitable solicitation statutes were generally written in the 1960s for direct mail and door-to-door solicitations.  They have not kept up with changes in technology, and the regulators have a great deal of difficulty dealing with this kind of solicitation.  The state attorneys general agreed in the “Charleston principles” many years ago not to recommend prosecution for charities that have a “passive” website that can accept contributions if the charities don’t actively drive people to the site or actively solicit in the state.  They might apply that recommendation to the first gift obtained from within a state on a crowdfunding site.  But once the recipient says thank you and asks for more, that would be a new solicitation subject to registration.

The fact that those who are soliciting on a crowdfunding site don’t seem to register doesn’t mean that they don’t have to.  It may just mean they haven’t been caught.

UPDATE 2/2023

More state charitable solicitation regulators are taking the position that having a "donate now" type button on a charitable website constitutes solicitation in their state because anyone in their state can find the website and be solicited for a contribution.  Registration may be required even though the charity never sends a specific solicitation into the state.

California passed a statute in 2021 to regulate crowd funding sites starting in 2023.  The state has been unable to develop its regulations, however, and it is not currently enforcing the registration requirements of the law. Certain prohibited acts, such as diverting funds or making misrepresentations in the solicitation, are in effect.  (See Nonprofit Issues, California to Regulate "Charitable Fundraising Platforms", Vol XXXI, No. 3.