Are you familiar with the term lobbying and how it shares a bedroom wall with bribery? Individual votes usually matter little to none in the grand scheme of things, and there's next to no evidence that politicians above the local level give a shit about individuals throughout a huge swathe of the US. Governatorial election promises in the southeastern US are almost universally lies about quality of life improvements, from healthcare changes in florida benefitting no one to roadwork that never happens being promised every election cycle in alabama and mississippi. There is a HUGE disconnect between representatives and their constituents in these states, and they're not the only ones.

Realistically, that money is not being used effectively to sway anyone, especially when little is actually used for propaganda, and weak vectors are chosen. Many campaigns are still running on outmoded methods of contact, like outdated lists of people for cold mailing, text messages that wind up in your spam filter, and shock value ads that only serve to annoy and change VERY few minds about anything.

You have a very optimistic outlook on how any politician views a letter or email from a constituent. Within my whole lifetime, I cannot name ONE politician in the US that has changed course over constituent contact. Not for any single thing. That's why someone asked if you were eight years old earlier; most people from 25-40 years of age have, at this point, accepted that the current system does not operate in the way that we were taught in school. Instead, we have this broken system where the cries of the masses enter the void, and MAYBE ONE "representative" echoes them to a person or place where change can begin. The ones that do are decried so unbelievably fast it makes your head spin, and the ones that retain office while doing so are treated like crazy extremists by any media that could inform people of their goals, so there's no hope of popular/uninformed support.