Why policies that poll well, are rarely implemented.
There's reasons as to why policies that poll well, don't end up translating into actual implementation, that don't get talked about nearly enough.
The first one, is the issue of actual turnout when the policy in question is actually put up to a vote. Polls don't determine what the government does: Turnout does. To highlight this, lets establish a hypothetical:
1000 people are surveyed about whether or not they support X policy. 650 people say they support it; 350 people are against.
Now, the policy is put up to an actual, official vote.
Out of the 650 people who expressed support in the survey, only 163 people actually show up to vote. But for the opposition group, 263 people showed up.
The opposition ends up winning, and gets the policy shot down; despite the polling suggesting that it should've won.
This highlights the critical flaw in using polling to gauge support for a policy: It's not how the government actually gauges what the public does and doesn't want. They look at who's actually showing up.
The second reason, is that voting isn't the end-all-be-all of the decision making process. This is the case in any democracy that I know of; and it is certainly the case in the USA.
One major roadblock that stops the government from building infrastructure quickly and cheaply, is how we handle our environmental review process.
There is no cap to how long it can take. There is no cap to how long the community input period is. We let projects get sued by opposition groups endlessly, until they successfully dilute or outright kill the project.
So when the government proposes, say, turning part/all of a thoroughfare into a BRT/LRT route, or adding in bike lanes, the government is forced to go through that whole exhaustive process; even if there's already a plethora of evidence stating "this is net-positive". And the opposition within the affected area tend to come out in FAR greater numbers than the supporters; further lengthing the time between planning and implementation. And if the project manages to get past all of that: The opposition can just sue the government and try to force it to so XYZ thing to "satisfy" them; further extending the planning period, and implementation period. And all of these things help to balloon the total costs of the project.
And even beyond the community review part: Opponents to a project typically organize far more to oppose even the idea of it, than supporters do. Negative emotions are far stronger than positive ones. And this also translates into votes; which means that they'll end up holding much more power to determine who ends up in office. This disincentivizes potential candidates who support such projects, from running; resulting in candidates who'll support what the opposers support.
And even if the voting doesn't stop such a candidate from winning: The opposition tend to consistently show up to place pressure on the elected official to drastically change their plans, or outright cancel them all together.
A third seldomly mentioned reason, is that certain policies, when the costs to the individual are pointed out, tend to drop significantly in support.
Support to build more housing polls very well; but support craters when the individual costs are mentioned. Single-payer healthcare is also a policy that sees support crater when the costs are mentioned. And as seen in that single-payer survey: Even when the benefits are mentioned, it is a near perfect split between opposition and support.
Now, combine that with the previous two points made, and it becomes even more evident about exactly why a policy that is stated to poll well, ends up not actually getting implemented.
The overall lesson I am trying to instill here, is that it is CRITICAL that those who support XYZ policy, to actually go out and participate in the decision making process to get it implemented. The government doesn’t listen to those who stay home; they listen to who is the largest and is most consistently placing the most pressure on them to do something.