Why wouldn't they.
Chinese are expected to moderately expand their arsenal, but they don't need significantly more silo-based warheads for credible deterrence, they just need to increase survivability from decapitation attack. Missile sponge is very cost effective way to do that. Their road-mobile and rail-mobile DF-41 ICBM's provide already good deterrence, but putting the new DF-41s into silos just increases the variety and survivability of their ground based deterrence.
Not a problem for China with its industrial capacity larger than both USA, and Russia together.
The biggest gun you can afford is almost always the most efficient spend of your money.
> they don't need significantly more silo-based warheads for credible deterrence
Who said they need it for deterrence? If their goal would be just deterrence, they wouldn't be trying so hard to undermine it.
It's very clear they want to have enough missiles to perform a first strike on the two likeliest (now possibly three) enemies.
It's the most clear, and logical explanation standing any military theory test.
Nuclear proliferation is extremely dangerous, for every one in the world including the proliferater, so it's not clear that a country maximally expanding its nuclear arsenal is the most logical move to advance its self-interest.
It's outright stupid to think that the person doing something something as big as this is not conscious of this.
On the opposite, this big scare factor very much must be a part of the strategy.
Arms control experts seem to think that China is building missile "sponge". Field of 120 silos would contain only 12 ICBM's or so. If they build enough silos into the desert and and decoys for the rest, the US must spend more and more missiles to destroy just few missiles.
The US had similar plan at the beginning of the Cold War. It became politically impossible to use eminent domain to create so large missile fields on farmland.