When someone searches for a solicitor, they're usually stressed, time-poor and comparing three or four firms at most. Being in that shortlist is what law firm SEO is for - and it's decided by a mix of local visibility, practice-area relevance and the trust signals that make a person hand you the most important problem in their life.
The difficulty is that every firm's website says the same things: decades of combined experience, client-focused approach, no-win-no-fee. Google can't rank two hundred identical claims, so it ranks the firms that prove theirs - detailed practice-area content, genuine expertise on display, strong reviews and a local presence that's actively managed rather than merely claimed.
Legal content is also YMYL, judged by Google's strictest standards - which suits well-run firms perfectly, because you have the real credentials most content on the web lacks.