A few reasons:
- CAP is one of the most iconic stadia in club rugby. How many others can boast a city centre location surrounded by pubs and five minutes from the nearest transport hub?
- Structurally it's good for another 12 years without any major works needing to be done.
- Its 13,000 capacity is good for all but a few matches it would play over the course of a season
- Contrary to popular rumour, it is possible to redevelop the stadium to a larger capacity and retain ownership
- CRFC have an agreement with the Millenium Stadium for four matches to be played there per year. Sufficient, you would have thought, for all of their marquee matches.
- CRFC currently make revenue from the car park, the on-site clubhouse and bar and the ground's conference facilities. This equates to about £700,000 per year, with a ground rent of £100,000. Compare this to the almost £500,000 they will be paying CCFC for the rental of Leckwith for 18 matches per year (many of which will see around 7,000 people showing up in a 23,000 capacity stadium. CRFC will not be able to earn any non-matchday revenue from Leckwith. Furthermore, the rugby club are locked into this deal contractually for five years, regardless of gates and income. If their business models are wrong, they will still have to cough up the half a million a year.
- CCFC will be the sole owners of Leckwith, and hence will have full control over branding, advertising and marketing.
- CRFC will be forced to split, with the Region going to Leckwith and the Welsh Prem side continuing at CAP, at least until it's sold off

- CCFC, as landlords, are able to terminate the contract after five years which, if CAP is sold off, would leave the capital's rugby team homeless. This is far more likely, apparently, if CCFC get to the prem (which is another reason I'd be happy to see them stay in the championship) due to certain premiership requirements applying.
- Bristol, the current GP strugglers, are currently on the edge of financial meltdown and administration. One of the most resounding reasons cited for their difficulties is the fact that they do not own their own ground, and instead rent from Bristol City (?). Given that gates and TV revenues are lower in the Magners than the GP, why on earth would another club want to adopt that business model?
It all stinks to high heaven. Looks to me like Peter Thomas, alongside his buddy Paul Guy, have their beady eyes on the prime real estate that is CAP. Rumour has it that it would be redeveloped into a hotel and media suite, which would be attached to the Millenium Stadium. This in turn would allow the city to attract events such as the Champions League and UEFA cup finals (apparently a media centre and accommodation are key stipulations for hosting such events), which is why in turn the City Council are tacitly supporting the move as it would bring revenue into the city centre, (and doubtless some tasty kickbacks if it ever occurred). Even though the land was gifted by the Marquis of Bute, and has a covenant limiting it to recreational purposes, I can't imagine that stopping such voracious capitalists in their eternal quest for cash and 'progress'.
So, in summary, CRFC have nothing to gain, and masses to lose, up to and including their own existence as a top level rugby side.
Further information here, should you be interested:
http://www.calltoarms.org.uk/news/20070924_2.php