Because they can't, the amount of Dev time spent on Starcraft MP is dev time not spent on it's SP, one or the other will always take precedence over the other and the "other" will be lesser for it.
Also Starcraft has a massive dev team compared to Battletech and there are just not enough devs for the people whom want this games to cover 3025-3075 in one long continuous SP experiance and to develop and support a competitive PvP scene, one or the other will have to be secondary objective and I vote that its MP that be the second.
My replies was toward the many people who keep saying that having both a great single player and multiplayer experience was incompatible. I believe the StarCraft franchise and the Civilization franchise are both amazing example on how this is possible.
Now, if you want to go into size and resource, sure, it makes things more difficult but again, not impossible. Taking the original Starcraft as an example once more, it was made by a team roughly similar in size to the HBS BT team, 50 people to be more precise.
As for the last bit of your post, you state :
... for the people whom want this games to cover 3025-3075 in one long continuous SP experiance and to develop and support a competitive PvP scene, one or the other will have to be secondary objective and I vote that its MP that be the second.
Now, this is where I believe our views differ.
Keep in mind that in its current state, BattleTech is missing both features from it's SP and MP components that were promised as part of the kickstarter.
All we, the MP bunch, are asking for, is that both the SP and MP be finished as it was supposed to be.
What some(not all of them) of the SP crowd, seems to be asking for, is to have DLC development takes priorities over MP features that are missing from the game at the time of this writing. That's a whole different story and one I have a problem with.
Don't misread this, I want multiple DLCs and sequels for BattleTech, I've been in "love" with this franchise since the early 90s, but I firmly believe that the priority should be given to what's missing from the final product and not for adding extra content to it, not yet at least.
If you look at who's is generally in favor of the MP being finished as it should, you'll see that these people, including myself, have the kickstarter backer icons attached to our PDX account. Basically, we're just asking to get the product for which we invested money at in the first place, meaning both the SP and MP features that are still missing.
I want to be clear, this isn't me saying I have priority over non backer, this is me stating that backers did invest their money into a product that as yet to be fully finished and that's all we really want.