Some IP addresses are unreachable due to invalid route

I want to connect to remote machines. The problem is that I can connect to every machine except one. After some invertigation I found that problem is in route. Here is example:

PS C:\Users\Alex> tracert 172.17.56.66

Tracing route to 172.17.56.66 over a maximum of 30 hops

  1    31 ms     9 ms    12 ms  10.19.64.1
  2     9 ms    14 ms     8 ms  172.17.56.66

Trace complete.
PS C:\Users\Alex> tracert 172.17.56.68

Tracing route to 172.17.56.68 over a maximum of 30 hops

  1    13 ms     7 ms     7 ms  10.19.64.1
  2    10 ms     5 ms     4 ms  172.17.56.68

Trace complete.
PS C:\Users\Alex> tracert 172.17.56.70

Tracing route to 172.17.56.70 over a maximum of 30 hops

  1    <1 ms    <1 ms    <1 ms  192.168.0.1
  2     8 ms    41 ms     7 ms  188.170.9.10
  3    96 ms     1 ms     1 ms  192.168.1.1
  4     1 ms    <1 ms    <1 ms  10.90.40.41
  5     1 ms     1 ms     1 ms  10.90.40.34
  6     1 ms     1 ms     1 ms  10.90.40.32
  7     3 ms     8 ms     2 ms  10.90.35.80
  8     *        *     10.90.35.78  reports: Destination net unreachable.

Trace complete.

I don't know why it handles this IP differently. Here is my route print.

===========================================================================

IPv4 Route Table
===========================================================================
Active Routes:
Network Destination        Netmask          Gateway       Interface  Metric
          0.0.0.0          0.0.0.0      192.168.0.1    192.168.0.239     35
     10.19.84.212  255.255.255.252         On-link      10.19.84.214    311
     10.19.84.214  255.255.255.255         On-link      10.19.84.214    311
     10.19.84.215  255.255.255.255         On-link      10.19.84.214    311
        127.0.0.0        255.0.0.0         On-link         127.0.0.1    331
        127.0.0.1  255.255.255.255         On-link         127.0.0.1    331
  127.255.255.255  255.255.255.255         On-link         127.0.0.1    331
     172.17.56.65  255.255.255.255     10.19.84.213     10.19.84.214     55
     172.17.56.66  255.255.255.255     10.19.84.213     10.19.84.214     55
     172.17.56.67  255.255.255.255     10.19.84.213     10.19.84.214     55
     172.17.56.68  255.255.255.255     10.19.84.213     10.19.84.214     55
     172.17.56.69  255.255.255.255     10.19.84.213     10.19.84.214     55
     172.17.56.72  255.255.255.255     10.19.84.213     10.19.84.214     55
     172.17.56.73  255.255.255.255     10.19.84.213     10.19.84.214     55
      192.168.0.0    255.255.255.0         On-link     192.168.0.239    291
    192.168.0.239  255.255.255.255         On-link     192.168.0.239    291
    192.168.0.255  255.255.255.255         On-link     192.168.0.239    291
        224.0.0.0        240.0.0.0         On-link         127.0.0.1    331
        224.0.0.0        240.0.0.0         On-link      10.19.84.214    311
        224.0.0.0        240.0.0.0         On-link     192.168.0.239    291
  255.255.255.255  255.255.255.255         On-link         127.0.0.1    331
  255.255.255.255  255.255.255.255         On-link      10.19.84.214    311
  255.255.255.255  255.255.255.255         On-link     192.168.0.239    291
===========================================================================
Persistent Routes:
  None

So after I added it statically (based on 66 and 68 gateway)

route ADD -p 172.17.56.70 MASK 255.255.255.255 10.19.84.213

It worked. But why does gateway detect automatically in other cases, but in this one I should hardcode it?