You have over 50 subscribers after 48 hours. What's the problem? Poles have their own instance yet the Warsaw community !wwa@szmer.info only has some 250 subscribers after 5 years. Lemmy is just small and only a few of the 50k MAU (about 10 of which are Czech) will be interested, you have to promote the fediverse (especially in the Czech Republic) first.
Did you know there used to be Czech instances czech-lemmy.eu and kyberpunk.social that barely saw any activity?