There should be less BBC in this modern world, not more
An easy to answer question:
Why is the BBC struggling to be more commercial?
The BBC does not face commercial incentives therefore it is not going to act commercially. Incentives do, after all, matter.
The more specific complaint here is that Amazon, Netflix and the like are pouring money into commissioning TV shows. The BBC is thus limbering up to insist that we should all be taxed more so that they, the BBC, can compete:
The fear now driving the BBC is that support for the licence fee could decline as new subscription players flourish. The licence fee is due a mid-charter review in 2022. Some rivals suspect the BBC’s doom-mongering is laying the ground to appeal for an increase as commercial efforts struggle.
The answer to any request for more of our cash is no. Instead, we should be reducing the licence fee, even selling off the BBC itself, turning it over to a subscription system, perhaps.
For why does the BBC exist? In order to provide what a commercially and market driven media landscape will not provide. Now that we've got those things being provided by a purely commercially driven media landscape there's no reason for the BBC is there?
Sure, and so comes back the argument, but there are still things which commerce doesn't provide and which taxpayers should. We don't believe so, unless "taxpayers should" there is to mean things the respondent likes but no economic analysis would support producing at all. But, OK, take that argument as being fair enough. That means the BBC shouldn't be producing things which compete head to head with those commercial organisations, doesn't it? Because they are already being produced and the BBC exists to produce those things which aren't.
That new tech means billions being poured into content production is not an argument for a larger or richer BBC, it's instead for one that is, at very best, reduced to a rump filling in the remaining gaps of market production. For that has always been the justification in the first place, producing what the market won't or doesn't.