But what you say, "net loss", is a huge generalization.
The economic study is also that kind of model that only generally describes it - but ultimately, doesn't draw lines in how colonies were profitable. There are quite a few caveats, one of them being the fact that administratively colonies were able and did press locals in forced/lower paid labour or outright imported works (Africans to America, Indians to South Africa) to lower price of labour.
Moreover, "net loss" is still quite not perceptable from that data. You can argue that state had to pay for colonies quite a bit, but it also had returns from capitals that operated in colonies and paid taxes in London; in fact, the profits of private capital that later returned as even bigger investments in Britain was what carried it's industry even when it wasn't most competative in the world.
Not just that. Exactly because the colonies were "net profitable" and were both markets for consumption and resources wells, they bloated directly and indirectly GDP of metropolitan area, increasing it substantially.
I mean, come on, the latter was a reason why for example German Empire wanted the colonial pie.
The very reason why the colonialism fell apart was essentially because Eureopean colonizing powers lost a few things:
- Industry that would be able to profit from exports to colonies. It was seriously in grieve state after WWII and it was a reason why India was no longer an asset they could hold and benefit from, but they still kept rest of territorial possesions and considered holding into them.
- Investments. As the economic model implies, the lack of investments due to near-bancrupt state of Empire (and probably very poor finances in private sector) as well as high taxes heavily limited ability to invest into colonies, thus making returns from them rather limited.
- Cost of Upkeep. Now, British Empire was quite effective in keeping colonial administrations. Even with transportation, it didn't cost too much to run most colonies to justify their abandonment. What mattered was an ability to deter threats. British Empire could no longer deter threats of local population in British Raj going rebel, protesting and simply keeping intact their rule in any kind of long run. However, in Africa for example they felt rather confident until much later it became apparent to British Empire that dangers created by external factors (US and USSR) were no longer surmountable and would cost more in upkeep and struggle. Thus, they had to retreat from there.
The World Wars were the major issues for these factors. Arguably, it all boils down to economic capability of UK that was rather crushed in World Wars. First one clearly didn't destroy the colonial system, even if the other powers could easily rival British Empire or try to surmount it (Germany, US). In a way, you could say that WWII was an attempt by Germany to crush the colonial monopoly, again, and even though Germany lost war it effectively reached the desired goal of crushing colonial system, which benefitted most world economics and greatly cost British Empire in terms of it's GDP and economy size.
So, in my humble opinion, colonies were not a net loss. There are little reasons for them to be and, after all, it doesn't make much sense. They inflated GDP immensively (and not even in a financial bubble way), which is naturally a great gain for economy. It could be argued that colonial system made little incentive for economics to be competative, which is indeed the case, but it wasn't any kind of "net loss" thing. Even the linked economic study doesn't say that and it pretty much supports the idea that only when British Empire was hit by train called Germany, twice, the system became way less sustainable.
Way bigger reason was the fact that they invested in military build-up and attempt to be third superpower, creating nuclear capabilities from nearly zero, expanding naval bases, trying to keep up navy and so on - all in order to surmount threats of keeping up their economic empire which thrived on colonies and that could live on even without British Raj. That bet didn't play well, Suez happened and all investment in Imperial Grandeur was for naught, the Empire entered it's political nadir and was forced to acknowledge that it could not protect the colonial system that was one of bulwarks of it's power. All while France, Germany, Italy, Spain focused on rebuilding their economies and which paid off in making them way more competative in global market.
If British Empire somehow succeeded in securing position of third superpower and "won" Suez crisis, colonialism would hardly fall so easily at least for UK. Not just that, but even military expenses that killed British economy in late 40s and 50s would be seen akin to "glorius Stalin's deeds" where it would be justified for interests of Empire. If it succeeded... which in my opinion had some chance, depending on a number of factors.