It takes me 4.5 hours from Kalasin to Chong Chom. It is about 30 minutes crossing the border. Free luggage allowance.
Likewise, it then takes 2.5 hours to Siem Reap. Total is 7.5 hours.
If I was to fly, it is one hour to ROI Et airport from my home, arriving an hour before, plus luggage fees.
I then fly an hour to Bangkok, then more often than not, a bus to the terminal. Faffing around another 20 minutes.
There I collect luggage in about another 20 minutes.
Then I must make my way to international departures and clear immigration, ensuring I am two hours at least before the flight.
It never works that way for connections, I am usually waiting 4–5 hours for connecting flight to Siem Reap, flight time to Siem Reap is another 1 hour.
Then I clear Cambodian immigration and collect luggage, at least another 35–45 minutes.
Then it's another hour in a taxi to Siem Reap.
Total 10 or 11 hours messing about, then the same farce on return flights.
And it's more expensive.
That's why we drive.