This is actually the first error of IT knobbers everywhere and has more to do with empire building, egotism and an inability to admit a gross error than any kind of common sense. As you have no doubt noticed.

The driving conceit that is used to justify all this is 'We are speshhhulllll and different and unique, and nobody else has ever wanted to run a multi-product multimedia CMS driven publication on the internet before so of course we need to write our own!' - a conceit fostered by the IT Director who gets an enormous team of flunkeys and a huge budget and makes him or herself indispensable by owning the enormous white elephant that (barely) keeps the company in business.

Any superior control is illusory, because the effort required to change anything is so great, the resources so comparatively limited and the economies of scale so completely absent, and in any case, by the time you can think of something completely that would give you a unique business advantage, and incorporate it into your bespoke system, 9 times out of 10 somebody out there in intyernetland has already incorporated it into one of the off the shelf vertical market products that did 90% of what the in-house developed tool was originally planned to do at a tenth of the projected cost back when development first started, and which has a current version that has a clear supported upgrade path from that then current version that now does circa 250% of what the bespoke CMS actually does and growing, whilst actuially costing a 20th of the actual cost of the bespoke 'solution'.

It makes about as much sense as unilaterally deciding to grow your own trees, mill your own paper, and mix your own inks in order to differentiate your magazine from the competition. And works just about as well...