It's nothing to do with being a "wimp" and everything to do with looking out for my wife and children (who are now grown up) whilst enjoying family holidays / weekends away. Pitch your tent on Great End on a beautiful summers evening and the following morning don't be surprised if you wake up to a howling gale and side ways rain. Not problem when you're 20 and away with your mates but it's not fair to inflict that on your young family. Or a girlfriend who's just getting used to the Lakes experience. It's all about thinking of others before yourself.
Living in South West London our time in the Lakes is limited. However by using the family car (and assuming we can get the time off) we can arrive in Langdale on the Thursday night and climb Bow Fell, Coniston Old Man and Helvellyn with all the flexibility that a bus could never offer us before heading home on a Sunday night. The only way to take maximum advantage in the beautiful Lakes is to use our car. After all that's why we pay our car tax! Not to mention stocking up on Lake District goodies from Booths on the way home. What's not good about that?
I would suggest that what's 'not good about that' is the impact on other people: I go to the Lake District quite often, and my impression of much of it is beautiful landscape, and beautiful towns and villages that are basically being ruined by the amount of road traffic. Bowness, Windermere, and the entire road between Windermere and Ambleside are often in a state of near-permanent slow moving and queuing traffic. Keswick is not as bad, but still often very busy, and much of the area around the town centre is much less pleasant because of it. The lakeside in Bowness is lovely if you look out to the lake, but basically completely dominated all day by traffic noise. And of course each additional car slightly worsens the problem. That's the thing about cars - when you choose to drive instead of going by some other means, you're usually - in effect - choosing to make your own life a bit more convenient at the expense of inconveniencing and slightly harming lots of other people. Most people, sadly, don't think about this, which is one reason why driving is so popular.
Now I should stress I'm not trying to pick on you in particular - it's just that your question was rather begging for this reply

I appreciate that for vast numbers of journeys, a car is the only reasonable means to make the journey, I have nothing against people who, after considering the alternatives, drive for that reason. And I have no reason to doubt from your explanation that your trips may well fall into that category.
Moving back towards the topic of this thread, it seems to me that there is a huge need to persuade more of the people who visit the Lake District to leave their cars behind (the alternative is either lots more congestion, or cutting more big dual carriageways through the landscape, and I doubt either of those would be very palatable). Re-opening the line to Keswick probably would help, but I doubt if on its own it would make a significant impact. It seems clear to me that even in Windermere, which has a reasonable and quite well-used train link and a pretty good bus network in the summer [*], the vast majority of visitors still choose to drive there, and I don't see that Keswick would be any different. I think what's really needed is a change in culture so that many more people start to understand the problems caused by cars, and become more prepare to make the effort to use public transport where practicable (which of course in turn would result in trains and buses becoming much more frequent to match demand. A virtuous circle

). And if there was some kind of transport authority for the Lake District (similar to TfL) that made sure trains and buses were integrated properly, and actively looked at ways to make it easier for tourists to leave their cars at home, that would help too. Without those things, I suspect those who doubt that reopening the line to Keswick would pay for itself or attract enough passengers to justify the cost may well be correct. But with those kinds of changes, reopening it would be a no-brainer.
[*] At least, when the buses aren't getting stuck in traffic jams caused by all the people driving, which in the summer seems to be quite often.