It's pronounced Checkia, not Chechia. How do you pronounce the 'ch' in Czech Republic? How do you pronounce it in Czechoslovakia? Why would you now pronounce Czechia so differently?
All those upvoters must have left their brains in the pub. Still, that's one way of approaching the weekend...
You're right, in that in this instance the 'ch' should be pronounced 'ck', but most people, me included, when seeing 'chia' automatically think 'ch' and not 'ck'. So the Czech people will have to contend with the rest of the world pronouncing their country name wrong. At the moment, when I see 'Czech Republic' I think 'Check'. It would take a humungous education effort to get the rest of the world's population to get the pronunciation of 'Czechia' right, as in 'Checkia'. That or the spelling needs to be changed to the latter so the rest of the world gets it right from day one.
All this doesn't even begin to deal with 'Cz' being pronounced 'Ch' (though most people seem to know that one).