Subsidies are part of the reason. Definitely not the whole reason, but part of it The Chinese provinces pump a bunch of money in to try to make their region's car manufacturers succeed. And every province is doing it. So you have a bunch of carmakers competing for market while being kept alive, so they do the most rational thing possible to gain share: lower prices.

Of course, they're also just good at building things since they do so much of it. And cheaper labor. Much better supply chain.

> China's EV subsidies are basically identical to US and EU subsidies.

Not really, not much similarities between China and EU subsidies past 15 years. China's NEV subsidies are illegal because they are either conditioned on illegal tech transfer, local content requirement, or restrict market access. To give a high level view of the problems:

1) forced technology transfer/IP theft -- all foreign automakers/EV battery producers forced to give up IP to access China's market (and subsidies). This was litigated before the WTO by the EU in 2018 (see WT/DS549):

  Hybrid in a Trade Squeeze, Keith Bradsher, Sept 5, 2011, NYT

  ... The Chinese government is refusing to let the Volt qualify for subsidies totaling up to $19,300 a car unless G.M. agrees to transfer the engineering secrets for one of the Volt’s three main technologies to a joint venture in China with a Chinese automaker, G.M. officials said.

2) Once foreign battery producers made IPR/IP concessions to access China's growing EV market and significant investment in battery production in China, they were effectively banned. All domestic, foreign automakers were likewise forced to switch to local champions, namely CATL/BYD, promoted by the gov't under MIIT's 2015 Regulation on Power Standard:

  Power Play, Trefor Moss, May 17, 2018, WSJ

  ... China requires auto makers to use batteries from one of its approved suppliers if they want to be cleared to mass-produce electric cars and plug-in hybrids and to qualify for subsidies. These suppliers are all Chinese, so such global leaders as South Korea’s LG Chem Ltd and Japan’s Panasonic Corp. are excluded.
  ... Foreign batteries aren’t officially banned in China, but auto executives say that since 2016 they have been warned by government officials that they must use Chinese batteries in their China-built cars, or face repercussions. That has forced them to spend millions of dollars to redesign cars to work with inferior Chinese batteries, they say.
  ... “We want to comply, and we have to comply,” said one executive with a foreign car maker. “There’s no other option.”

3) China also made sure no Chinese consumers had access to EVs with batteries from foreign EV battery producers effectively creating a captive market of buyers for CATL/BYD.

  Why a Chinese Company Dominates Electric Car Batteries. Keith Bradsher and Michael Forsythe, Dec 22, 2021, NYT

  The government soon said electric car buyers could get subsidies only if the battery was made by a Chinese company. G.M., which had not been notified of the rule, started shipping Buick Velite electric cars in 2016 with batteries made in China by LG, a South Korean company.
  Angry consumers and dealers complained that local officials were denying them subsidies, people familiar with the episode said. G.M. switched heavily to CATL for the huge Chinese market.

4) another fairly recent example of China's arbitrary regulatory barriers to keep out foreign competition, which was later dropped after the gov't found out their local "champion," CATL, couldn't pass the EV battery safety test:

  Why a Chinese Company Dominates Electric Car Batteries.
  ... A rival had released a video suggesting that a technology used by the company, CATL, and other manufacturers could cause car fires. Imitating a Chinese government safety test, the rival had driven a nail through a battery cell, one of many in a typical electric car battery. The cell exploded in a fireball.
  Chinese officials took swift action — by dropping the nail test, according to documents reviewed by The New York Times. The new regulation, released two months later, listed who had drafted it: First on the list, ahead of the government’s own vehicle testing agency, was CATL.

So these are very deliberately orchestrated mercantile policies to gain advantages with forced tech transfer, limited foreign competition, and subsidized overcapacity and export subsidies. It's just too bad that the existing global trade/subsidies regulation regime, aka, the WTO, doesn't have much effective enforcement tool to discourage/punish such behavior. EU's shortcoming IMO is their blind faith in the market and their belief that the market would autocorrect.

As of this week, EU has over 100+ countervailing measures (anti-dumping/anti-subsidy) in force against Chinese imports, ranging from ceramic tiles (AD560), to decor paper (AD712), to polyester yarn (AD690); in addition to few more dozens of on-going investigations from candles (AD726) to hardwood plywood (AD717).