I also think that travellers aside there are several factors that result in us not getting aires.
UK folks are generally getting more selfish and disrespectful of our shared spaces. Everywhere I look people leave a mess, it isnt just travellers (although their mess is usually something quite horrible to behold). Any beauty spot after a sunny day will be covered in litter, sometimes whole campsites left behind.
Costs in the UK often result in aires being unattractively priced if they were private, there isnt much desire with tight budgets for councils to put some in place (although some are allowing you to park overnight now).
Constant articles of late and perceptions that motorhomes are bad (not just travellers). Residents generally seem to consider them a blight not a boost. NIMBY is a very British concept I think. We like renewal energy, campervans, etc as long as its nowhere near where we live.
There is a perception that there isn't space, one I don't think is based on facts. The reality is that 2% of the UKs land mass is built upon... but because we live in that 2% we perceive its all built on.
The closest Ive seen is the likes of Dartmoor Halfway Inn, a pub with a campsite bolted on. This is a setup I am really loving the more I find. Late check in possible, usually affordable and food if you need it. More pubs with stopovers would get my money