They tried the more complicated route before they tried the simple route? Assange was in the UK for approximately two years before he went into the embassy.
Edit: HN doesn't let me reply so deep in a thread unless I wait like 20 minutes. It'd have been simpler if he were detained as they'd have had a guarantee of his jurisdiction and plan accordingly. I imagine having him arrested in a country that had allowed CIA extraordinary rendition would've been better for them than having him protected in Ecuadorian embassy.
[1]: https://www.smh.com.au/world/europe/wikileaks-founder-julian... [2]: https://www.theguardian.com/media/2018/nov/16/julian-assange...