Tom, you are right that the public's concern with Ukraine is not a natural occurrence: It is the result of the attention the media and government are giving it. That said, there are valid reasons to care more about Ukraine than about Yemen:
1) Ukraine is in Europe, and Europe is simply more economically important than Yemen. Affairs that affect Europe have a wider impact on the world economy and are of more concern to our allies.
2) The Saudi government's actions were basically being taken without substantial international opposition.
3) Ukraine is being attacked by a major power that has developed close ties with China. That China's military budget, which on a purchasing power parity adjusted basis has just matched the US's, is scary also naturally produces concern regarding the aggressive actions of her allies. It is possible China is supporting Russia's actions to test the West's resolve regarding Taiwan.
4) Political action taken by this China-Russia "Belt and Road" alliance is more troubling than action taken by Saudi-Arabia because China and Russia both have nukes.
5) Putin's move on Ukraine likely portends moves on other former Soviet Bloc states while the conflict in Yemen is basically isolated and unlikely to spread. If Putin were to set his sights on a NATO member, the consequences would be world altering (and not for the better). If a high price can be extracted for invading a sovereign state, this nightmare scenario can be deterred.
6) Ukraine is obviously more important economically and strategically than Yemen is.
7) The taking of Ukraine would mean that Russia and Poland would share a border: While NATO was already abutting Russia because of the Baltic members, Poland's hostility to Russia is greater largely due to its unfair treatment under the Soviets, massacres like that at Katyn, and the historical hostility caused by Russia's wars on the Polish-Lithuanian Commonwealth. (Read Putin's essay on "The Unity of the Russian People" and you will see his hatred for Poland comes in loud and clear.)
8) This war will affect natural gas and oil supplies
9) This war will negatively affect the world’s food supply, causing foot shortages in North Africa and the middle east that could be very destabilizing.
10) This is more likely to escalate into a nuclear conflict.
You, of course, know all this: So I am a little surprised to see you making this point. Yes, people's concern is a function of the media and government attention this has gotten, but there are rational reasons for that government and media attention.
NATO expansion beyond that first wave was almost certainly a mistake (though if Poland were not a NATO member, Poland would probably be at war with Russia now---with consequences that would be hard to foresee but would likely not be good.) However, as in Chess, sometimes after you make a bad move your best follow up moves can also be somewhat ugly.
One last point, which is that if it were not for NATO expansion, it is hard to believe nuclear nonproliferation would have been as, imperfectly I admit, successful as it was. Indeed, Ukraine likely made a mistake and should have only given up its nukes in exchange for NATO membership---if at all.
For #1, maybe "more spiritually, culturally, and economically important" (and any other adverbs that come to mind). Or just substitute "better" for "more economically important" and "anything non-European" for "Yemen".
Or you can just say that Europeans should care more about European stuff than about non-European stuff.
Of course, non-Europeans should also care more about European stuff than about non-European stuff, but it would sound kind of rude to assert this even though it's true.
Isn't Ukraine pretty much the Proto-Indo-European homeland or at any rate the western half of it? That seems relevant too.
FYI, I no longer think NATO expansion was a mistake. We actually needed to expand.more aggressively.