In what way don't they achieve anything? This year's Tonga tour drew a combined TV audience of over 2 million, and had just under 40,000 paying spectators. It also ensured that England actually had a presence locally, which is the only way they'll ever grow the England brand (it's also the only way they can actually attract sponsors to the brand)
Whilst the Tonga tour could have been more successful, the fact that there is already positive talk about Samoa going over (BBC has expressed interest in broadcasting again, we have bigger venues wanting to host like Wigan, Hull, venues in London, etc) shows that there is value.
Also if we ever want internationals as a whole to grow, we need for more than the NRL, RFL and NZRL to be able to pay their way. Tonga received a tour fee for going over to England (none of the nations in the Pacific Championship received any appearance fees), which now gives them the ability to invest into something (whether they do or not is another question).
As
@titoelcolombiano said, we have a responsibility to support England from an international front. Letting them die, or forcing them always to tour Australia & NZ is not only selfish, but shrinks the already small world that is international rugby league.