A lack of competition aka mono/duo/oligopols controlling markets is obviously unhealthy, because too large and powerful entities can and will gouge customers in the best (=most harmless) case, or actually make absurd demands from politics in the worst case when they get way too large (see the recent Credit Suisse bank scandals).
The other way around, too much competition, is also bad, as it incentivizes unhealthy business behaviors such as wage theft, tax evasion, barely making profits (and thus, having no reserves for the event of an externally-caused economic shock), or exploiting customers to the point that they rather piss into a bush (and annoy residents) than pay 50ct for a loo.
And to make it worse, a part of the problem is that there are a ton of gas stations - in Germany, about 14.000 [1] - but only a handful of oil suppliers. And the suppliers have an insane amount of leverage here: the gas stations are effectively locked to them (e.g. virtually all oil in Eastern Germany originates from two refineries in Leuna and Schwedt), so the refineries can charge whatever they want, and gas stations don't have the freedom to add markup to make profits on gas.
[1] https://www.adac.de/verkehr/tanken-kraftstoff-antrieb/deutsc...
The core problem is, as so often these days, that decades of unchecked capitalism have "optimized away" resilience on all levels: first, too much competition led to gas stations depending on concession sales (while oil companies make ever more insane profits), and now gas stations depend on nickeling-and-diming customers for shit that used to be free (by exposing them to ads wherever they can, some places have gated their vacuums and air pressers behind payment, and good luck finding a free loo). It's going to be a real shitshow when the ad companies shut down as the advertisers are cutting back on budget.