Eh?
If it is so easy and convenient, why can't I buy it when I buy my ticket to go into london for the day by train from my local train station?
If it is so easy and convenient, why does it cost £10 to get a refund on unused credit? Why cannot I just put on the card enough for the journey I plan to make, for example. Why, for example, cannot I just use the Oyster card and have the cost of that journey direct debited from my account?
If it so easy and convenient, why can't I buy one from everywhere I can buy a paper ticket?
If it so easy and convenient, why do I have to plan in advance to get an Oyster card as opposed to turning up and paying for the journey when I need to.
If it so easy and convenient, why do I have to remember where I put the card last time I used it 6 months ago .
If it so easy and convenient how can I find out much is left on it so I dont have to go to a ticket office to top it up (just like going to a ticket office to ........oh I dunno.......buy a ticket for example)
Basically it is easy and convenient for those who use TFL services on a daily basis and know how much per month they need to put on the card. For the rest of us in the rest of the country who come to London irregularly or infrequently it is no more convenient than buying a ticket (and usually less so because I can conveniently buy a paper ticket as part of my rail fare). I suppose that is why they have made the ticket prices really expensive, to try to force all of us into buying the card, 'cos there is really no other reason to do so.