Well they are rolling out Digital Billboards that have a 12 year life (as far as depreciation policy is concerned), and want to beat the competition to as many locations as possible. There are also lots of smaller operators of static billboards who can divest and split the value uplift with QMS (or competitors), which creates longer term dividends. There is also the potential for new technology and arrangements that can squeeze more out of these sites.
So as this is the case, while there is net operating cash being generated, this, and more, is being invested back into the business as you can see in the negative net investing cash in the latest HY report. So this is probably the wrong investment for an investor interested in dividends now. (And has been the wrong investment for many who wanted a capital gain too - lol - hopefully we get some joy soon in that regard - who knows?)
