CryptoNight relies on random access to the slow memory and emphasizes latency dependence.

Each new block depends on all the previous blocks (unlike, for example, scrypt). The algorithm requires about 2 Mb per instance: It fits in the L3 cache (per core) of modern processors.

A megabyte of internal memory is almost unacceptable for the modern ASICs.

GPUs may run hundreds of concurrent instances, but they are limited in other ways.

GDDR5 memory is slower than the CPU L3 cache and remarkable for its bandwidth, not random access speed.
Significant expansion of the scratchpad would require an increase in iterations, which in turn implies an overall time increase.

"Heavy" calls in a trustless p2p network may lead to serious vulnerabilities, because nodes are obliged to check every new block's proof-of-work.

If a node spends a considerable amount of time on each hash evaluation, it can be easily DDoSed by a flood of fake objects with arbitrary work data (nonce values).

 List Of cryptonight Coins 2018 : 

 Monero
Algorithm :CryptoNight
Minable: Yes
Prooftype:PoW
Market cap :$4,974,084,431
USD PRICE : $315,87


Bytecoin
Algorithm :CryptoNight
Minable: Yes
Prooftype:PoW
Market cap : $946,712,054
USD PRICE : $0,00515

 Electroneum
 Algorithm :CryptoNight
Minable: Yes
Prooftype:PoW
Market cap : $490,134,296
USD PRICE : $0,07876

 DigitalNote
Algorithm :CryptoNight
Minable: Yes
Prooftype:PoW
Market cap : $151,529,593
USD PRICE : $0,02197

 Aeon
Algorithm :CryptoNight
Minable: Yes
Prooftype:PoW
Market cap : $57,517,830
USD PRICE : $3,71

 Sumokoin
Algorithm :CryptoNight
Minable: NO
Prooftype:PoW
Market cap : $7,776,624
USD PRICE : $2,75

 Karbowanec
Algorithm :CryptoNight
Minable: Yes
Prooftype:PoW
Market cap : $6,125,479
USD PRICE : $1,14

 Dinastycoin
Algorithm :CryptoNight
Minable: Yes
Prooftype:PoW
Market cap : $2,454,048
USD PRICE : $0,00164

 LeviarCoin (Pre-Launch)
Algorithm :CryptoNight
Minable: Yes
Prooftype:PoW
Market cap : $2,081,483
USD PRICE : $0,19323

 Fantomcoin
Algorithm :CryptoNight
Minable: Yes
Prooftype:PoW
Market cap : $1,772,410
USD PRICE : $0,25495

 QuazarCoin
Algorithm :CryptoNight
Minable: Yes
Prooftype:PoW
Market cap : $289,584
USD PRICE : $0,04249

 BipCoin
Algorithm :CryptoNight
Minable: Yes
Prooftype:PoW
Market cap :$238,550
USD PRICE : $0,14660

 Bitcedi
Algorithm :CryptoNight
Minable: Yes
Prooftype:PoW
Market cap : $160,211
USD PRICE : $0,02783