Yemen was supplied with high tech missiles and technology (including drones) to make more by nearby Iran. Venezuela has no such benefactors in their region (or anywhere globally really). Iran or China also provided them with intelligence to help in targeting US ships and doing interception of merchant vessels in the first place. Again Venezuela has no such powerful benefactor in the region, no supplier of arms, etc.
There's also the fact that the Yemeni people had a lot less to lose after all they'd been through than Venezuelan people and arguably had/have less compradors within their ranks to sell them out. Yemen also wasn't sitting on oil and the US already had strategic ports and airbases and so from the US point of view fighting them was a draining distraction without any possible reward while Venezuela together with Iran means control of world oil markets by the US empire.
There's doomerism yes but the flip side is people who stick their heads in the sand and make socialists look like detached from reality deniers by saying nonsense like the US and Trump would make up kidnapping Maduro.
That kind of thing drives people away from us. Being consistently correct will get people interested in how we think and entertaining our propositions but denying easily provable reality because we don't like it when it's actually provable makes our denials of their fabrications less convincing because we come off as sore losers. Sober analysis isn't some exact center between doomerism and cope and denial but it definitely incorporates an understanding of things being bad without tipping over into woe-filled proclamations of how the world is hopeless and doomed and we'll never escape capitalism and we need to nuke it all. That kind of emotional outburst isn't great even if I understand it. We need to have the strength to admit defeats and failures and not retreat into cope and wishful thinking about "here's how Bernie can still win" but applied to an anti-imperialist situation as well as to try and avoid maximizing doom by extending a regional defeat to the complete loss of hope for the world forever and other absolutist antics of despair.
There's also the kind of doomer who just parrots suspicious statements and accusations and probable disinfo that aren't penultimate proclamations of doom but empire narratives that are considerably more in doubt than things like claims of capturing someone which historically are not lies. Such as the one about Maduro agreeing to this and this being an arranged exit which is interesting to report on but shouldn't be seen as anything but odd fiction or disinfo to dispirit the bolivarian revolution until solid proof or reliable sources of some sort arises.