I cant tell you why everyone is disheartened with this move but i can tell you about me
I have played Warband for many thousands of hours across a few modes, There are a few things really that keep me coming back after so long.
My first love was crpg because it had massive battles of up to 200 players, They were exciting and i could sit on a teamspeak with 10-15 of my clan mates and have a great time laughing and joking and i would recognise and know most people on the server so it was a great sense of community, I still enjoy crpg with smaller numbers of course but the best times were the big battles.
Native battle was my second love after i started looking for a different challenge, although the battle size is generally smaller it holds the same challenge and sense of community, I can hop on IG Battlegrounds and have a good time with its 50 players and know quite a few of them, The native competitive scene is something special, community run tournaments based on battle that drive people to improve, 8v8 is for me a perfect number, it allows tactics and game play that is just impossible with smaller numbers.
I have played siege but i get bored pretty quickly and it wouldn't keep me coming back, there is no real tension for me with multiple lives and is a very casual mode
Battles with low player counts IE 5v5 6v6 i find get dry and boring also very quickly, when a server drops to that level you will find it can quickly drop to 0.
You say give skirmish a chance etc and trust in the Taleworlds but all I can see is them taking away the things I have loved about multiplayer, things that have kept me playing Warband for years and replacing it with things I personally do not really enjoy, multiple lives and small player numbers.
It sounds like the only way I will be able to play Bannerlord with my clan/group of friends is to play siege and that will get tiresome pretty quickly.
The main appeal and selling point of warband when you talk to friends about the game is "its cool you can have massive battles and sieges, imagine Age of Empires but your just one of the dudes" It conjures up something special in the mind, I just cant do that currently if anyone asks about Bannerlord.