How is Scrypt ASIC-resistant?
The Scrypt algorithm started out as an "ASIC-resistant" algorithm, but it isn't anymore.

Because it is highly memory-intensive, it was thought to be prohibitive to design and use ASICs for it. Initially it kind of was. With cost of memory decreasing and the necessary research put in -- in order to unlock the profit potential attainable using Scrypt-capable ASICS -- that ASIC-resistance has largely vanished.

A great many ASIC hardware projects for Scrypt started out with great fanfare, but only rather few have succeeded and ever been delivered. A rather large part failed along the way or were scams from the beginning, with developers pocketing money for pre-orders and never delivering any product. Despite these numerous frauds, a number of ASIC development projects have actually been completed and mining hardware has been delivered. As soon as a successfully completed machine was deployed and hit the market, this was always visible in a significant increase in mining difficulty for Scrypt coins whose profitability has, as a result, steadily decreased with every new ASIC model delivered.

The only residues of Scrypt being ASIC-resistant these days are the lower hash rates you see with Scrypt-based Crypto coins as opposed to SHA-256 ones.