Most people are capable of critical thinking, but that's really not the issue. The issue is the slow chipping away at people's ideas, beliefs, political alignments, caused by the rapid fire, high volume volley of headlines aimed at people.
For critical thinking, you first need to actually have an opinion and be invested in a subject. If you're not interested in vaccines but keep getting chips to the tune of "vaccines are bad", "vaxxines cause this or that", slowly your opinion will change.
If you zoom in to the individual then sure, critical thinking is important. If you zoom out to a society though, it doesn't really matter anymore. There are forces in play that know exactly what they're doing. They don't need to be right, they just need to chip away at people's beliefs and opinions.
And it's working; the US is an oligarchy run by rich nazis and headed by an ignorant scapegoat, the UK is leaving Europe and will be left poor, chaotic and vulnerable. Ukraine is a dictatorship. Russia, China and the US are freely suppressing or killing dissenters and putting people into concentration camps. And the world shrugs because what can they do? The powers that be are stuck in their status-quo; can't sanction the US or China because of trade deals; can't go against Russia because they'll help us win the elections. The list goes on.
Sorry, this turned into a bit of a rant that veered way off topic. Tl;dr critical thinking is not the problem, worldwide campaigns are, hundreds of impressions a year over multiple years are slowly influencing people.