I don't know what you did wrong, but I've had that experience too. They are fiends to grow - commercially grown stuff here is grafted in vitro to a tougher root stock (clianthus sp from NZ). Of course in the wild they are tough as old nails!

I have flowered them from seed, but I suspect that was luck as much as anything. They detest wet leaves.

Here is a link that might be useful: Don Burke's notes on swainsonia formosa

You just live in the wrong place!
Meanwhile the Canary Island Date Palm, much favoured in Victorian Era here, is on the edge of being an environmental weed, as it comes up by itself in the bush. You have your revenge!
I'm not sure that you'd ever get the Sturt's Desert pea to grow on any island anywhere. It likes to be a good long way from the coast, unless you happen to be fortunate and having a drought which is stripping the humidity from the air. Sturt's Pea is doing well here in Toowoomba at the moment.
I would imagine that on the Canary Islands you could grow lots of interesting plants from those parts of Australia where the desert meets the sea in Western Australia. Availability would be a problem, though - we can't even get them here.
Trish

I have seen these growing in my sisters garden in Gosford north of Sydney less than 10 klms from the coast. She had them growing in a large upturned concrete pipe filled with rubble and sand. They grew to flowering and also set seed, so it would seem that they can cope with a coastal climate. The Canary Islands would be significantly less humid, being adjacent to the Sahara Desert so I dont think that the climate was a factor.
My guess, though never having grown them, is a problem with the mix you used. They like infertility so avoid any mix that might contain nutrients, especially phosphorus, and water sparingly, and like Nathanhurst said avoid wetting the leaves.
As for the CIDP, I wasnt aware that they had weedy potential, but maybe not surprised. They do have a lot of fruit which I assume is transported by birds and bats, and considering that they are planted in every farm house garden they should have little difficulty in spreading around. I have seen them growing in Cornwall in SW England, but I cant imagine them becoming weedy in those latitudes...

Greg Kirby, at Flinders University in Adelaide did a lot of research into Sturt Peas with commercial markets in mind. Some of his findings were the opposite of what has been generally accepted when it comes to cultivation, including water and nutrition. The link below takes you to a Web site that gives some information from Kirby's research. Scroll through until you find the headings. This info has been printed and is available through the Australian Plant Society in SA at the Plant Sales.

Here is a link that might be useful: Sturt's Desert Pea

Alkalinity in the soil may be important, too. A Toowoomba gardener claims that his superb specimens are due to planting them in old besserbricks, where the lime leaching out of the concrete keeps the pH high.
Trish

I grow Sturts peas in Sydney as a party trick. I germinate the seed and plant directly into large pot with potting mixed 1:1 with coarse sand. Plenty of controlled release fertilizer for natives though. They will not tolerate root disturbance and are gross feeders. Once they start moving keep them going with thrive or similar. Regular Phos acid sprays are also a good idea. Treat them as an annual as very unlikely to get second flowering. It does happen but not often. Avoid overhead watering if possible, although they do tolerate it in a polyhouse for some reason. I do use a touch of lime though I'm not convinced of its efficacy. Also I find they last longer if I sow them in the autumn.

What gonow says is, I think, born out by Greg Kirby's research. Besides plenty of feed they also need water and apparently do well in selfwatering pots. Ants often carry the seed around so in some circumstances seedlings will appear in other spots in the garden. Today I potted on a dozen seedlings and have my fingers crossed as I left them a bit long to be doing this. Will know in a day or two if it is a disaster.