Maybe just be thankful for the fact that their players don't have to hold onto a day job outside of cricket unlike the pioneers for the other nations. There has been no nation in the history of the game that had their path paved for them like Bangladesh has, and the least that one could expect is for their vocal fans and players to be cognizant of the fact before thumping their chests.
While I agree with a lot of your post, I do have issue with this.
The pioneers of the game in other countries did not bear the same weight of expectations as the BD lads have. And they all have had benefit of solid domestic cricket infrastructure and exposure to top level cricket before gaining Test status.
It's very different to compare India's first International cricketers to BD's. They had solid experience behind them, played with little expectation and scrutiny, and didn't have to worry about disappointing millions of people if they failed. It was also never a question of 'return on investment' for them.
BD's first 15 years have been filled with raw youngsters with little to no experience being thrust into the international spotlight with high hopes and expectations; and not just of their own fans, but of the cricketing community as a whole.Everyone has viewed them as some sort petri dish in a lab experiment - 'We chucked millions of dollars into this developing country who love cricket, lets see how long it takes for them to become decent', and every time they failed there were hundreds of media outlets, pundits and posters on forums calling them a disgrace to International cricket, accusing them of wasting time and resources.
Imagine if that was done to a country like New Zealand when they were first trying to find their feet?
The players have huge egos because one the one hand, yes, they are highly paid superstars despite being mediocre cricketers...but on the other hand, every success is another big 'FU' to all the people who talked trash about their country and their side for as long as they have grown up. They have spent their lives dreaming of performing on the big stage and getting big wins - and now they have whitewashed 2 countries at home, made the KO stages of a World Cup, and are suddenly starting to develop a decent side and gain some respect. They are bound to feel quite a bit proud. And the fans probably feel much the same way tbh.