Many of these call centers are located overseas in countries such as India. Thy use VoIP services to be able to change their calling telephone numbers at will, and they routinely ignore the DNC list realizing that the US government won't make any real effort to track them down.

Non-profits are exempt from the DNC list. Organizations that have had a relationship with you are exempt. Companies that are not selling a product (surveys for example) are exempt. Political calls are exempt.

A telemarketer can claim to be conducting a survey to get around the law. They may ask a few questions to meet the letter of the law, but then they can break into their sales pitch...such as offering the sell or lease solar panels for your house.

Thank you for returning.
However, your explanation is ... um ... insufficient, and tends to prove you misunderstand the DNC rules.

Your "loopholes" are indeed exemptions.
1.  The DNC list is expressly limited to telemarketers.  Surveys and political calls are not telemarketers.
2.  Supposed surveys that are really sales calls are violations of the DNC rules.

Again, criminals / scammers / spammers ignore the law.
Can you tell me one law that is not ignored by criminals (no, do not cite the "law of gravity")

Telemarketers...shady ones...are exploiting the exceptions. As noted some can ask questions to be able to claim to be conducting a survey.

That is a loophole.

The spirit of the law is someone calls you, asks questions, thanks you for your time and then hangs up.

These telemarketers are bases overseas. I just received a call from one before typing this reply. When I anonymously called back, I heard a Iot of people talking some foreign language in the background. A second callback resulted in an answer by a woman with a thick accent. It sounded possibly Chinese.

These operations don't care about the law because the Federal Government won't make an honest effort to go after them. If these people are calling on behalf of an American company, the Feds can go after said company.

Received a call from this number on my cellphone, did not answer.  Not too many people
have my  number, amazing how the scammers can do this!