I'm not sure you have thought this through kittylister.
If we look at the Welsh Government, we can see Labour got exactly 50% of the seats. If they went forward with just their 50% it would mean they could govern. However, it would be difficult to bring forward and pass new legislation.
They have made an agreement with Plaid Cymru. They have looked at the bills most important to each party and then agreed which of them the Welsh Labour Government will bring forward. Having agreed Plaid will support Labour and vote for these bills. This is not a coalition, just an agreement.
Labour could win the next election but they could win it without a commanding majority. They could then make a similar agreement with the Lib Dems and the Greens, both Parties who have some aims in common with them. They would then look at each parties list of most important legislation and agree on a list they could work through. The smaller parties would agree to back Labour on these votes. They would not be in a coalition; the smaller parties would not have positions in the government but the parties in the agreement could move things forward.
There are reasons why centrists voters of all parties could see this as a way forward. They could negotiate with Labour and ensure the flavour of government was seasoned with their aims. Such an agreement is likely to leave out far-left legislation, at least for one Parliament. This could be good for all those parties and, in my view the country. What we cannot say is how long this could continue. Could it be taken into the following Parliament, for example?
I'm not sure if this helps. One other thing. For every one of you who would vote Tory if there was only Tory or Labour, there will be someone who will only vote Labour if the offer was the same. The parties on the left who want to work in common know this, which is why each of them will put more money into the most winnable seats. The Tories would have to fund more seats because they would be fighting against two or three parties. Not really "silly" at all.