They make big and numerous promises, setting the bar so high that they become slaves to their own promises. Freedom lies in breaking them.
Consider the Evangelical Christians I met in college. They claimed to love me and to care about you. That's a hefty promise. I doubted. You can't will yourself into loving me. It implies that you do not love me. You can declare love but you can't enter the state of love. The state of love is a consequence of people keeping it 100 to each other. If you were in that state of love, it would be pointless to say that you love me.
I decided to put them to test. Whenever I needed help, I reached out to them. I asked them to review my cover letters, resumes, articles asked them for rides (when I needed for real). Never did I ask them for anything that could cost them a lot of money or time. Still, almost all of them failed to help me even once. Over three years, I reached out to almost all Christians who had preached to me and had told me they loved me. A very small minority kept up their words. Those who had shown the most affection were the least likely to help.
The qualitative study excludes non-preachy everyday Christians.
But they had to make that promise to delude the naive. In college, I carefully watched a cult, the Southern Baptists. They are instructed to tell the gentiles that they love them to win their trust. They hope to then slowly build a relationship so eventually, they can preach to them. It is all a part of a bigger scheme. Hence, it is not the case that they can't back their words with actions, rather they delivered too many empty promises, to begin with, ensuring their failure to keep them.
Consider the US population, in general. The word "friends" has been used so lightly that it no longer means anything. That's why they now have two more terms "real friends" and "fake friends" to mean "friends" and "not friends". This development occurred solely because they are don't want to call someone "not friends" but you cannot have friends without not friends, just like you cannot have fit without fat. But this has not happened by chance.
In schools and colleges, there is an incentive to be nice. Unlike the real world, where you pick the truthful barber over the nice but shady one, in schools and colleges, nicety gets you more opportunities. Do we not know that teachers allocate all resources and opportunities to the students who obediently keep up with corruption and untruth? Do we not know that all who stand against the untruth are detained? Form an early age, it is established in the minds of the young that truth will lead them to failure. Why then, are we surprised that the finished products of these factories prefer nicety over truth?
To be nice, they must say that they care about you, that you are their friend, even though none of it is true. The education system has taught them to please people (boot-licking is a required skill for future corporate workers). They can keep everyone happy that way, so all opportunities will come floating to them. After all, this is how it happened in college. And it is good to be nice. Therefore, it is not the case that they can't back their words with action. They just run their mouths too much, spitting empty promises.