My understanding is there was an additional set of regulations that went into effect after the election “season” was over.
Short codes are typically a high priced option as there are a limited number of short code phone numbers available. All Application to Person (A2P) text sending (shortcode, 10DLC, or 1800) must now follow a lengthy set of compliance regulations: United States: SMS Guidelines | Twilio which typically includes an opt-in requirement. Though I should note that the opt-in can occur via a face-2-face interaction (Would you like to get text notices?) and doesn’t always have to be done via SMS.
I compiled a list alternative methods for SMTP to SMS message sending in an earlier post: Text notifications for Cricket customers--SMS vs. MMS - #2 by wesochuck These would function as a drop in replacement for the current Polaris service. We use MessageBee as others here have mentioned, though I’ve also heard good reports from some using Innovative’s service as well.