BGP Next Hop

BGP Next Hop

in the BGP configuration below, I am not sure why on R2 and R3 the next hop is not the IP address of R1 interfaces ,either( 192.168.12.1 or 192.168.13.1)
I mean on R2 to reach the loopback (3.3.3.3) of R3,  the Next-hop is showing the 192.168.13.3 and on R3 to reach the loopback(2.2.2.2) of R2, the Next-hop is showing 192.168.12.2
I thought the Next-hop should be the interfaces of R1either( 192.168.12.1 or 192.168.13.1)

I can ping 3.3.3.3 from R2 and 2.2.2.2 from R3

Thank you

R1#
interface Ethernet0/0
 ip address 192.168.12.1 255.255.255.0
!
interface Ethernet0/1
 ip address 192.168.13.1 255.255.255.0
!
router bgp 1
 bgp log-neighbor-changes
 neighbor 192.168.12.2 remote-as 1
 neighbor 192.168.12.2 route-reflector-client
 neighbor 192.168.12.2 next-hop-self
 neighbor 192.168.13.3 remote-as 1
 neighbor 192.168.13.3 route-reflector-client
 neighbor 192.168.13.3 next-hop-self

R2#
interface Loopback0
 ip address 2.2.2.2 255.255.255.255
!
interface Ethernet0/0
 ip address 192.168.12.2 255.255.255.0

router bgp 1
 network 2.2.2.2 mask 255.255.255.255
 neighbor 192.168.12.1 remote-as 1
 neighbor 192.168.23.3 remote-as 1

ip route 192.168.13.0 255.255.255.0 192.168.12.1

R3#
interface Loopback0
 ip address 3.3.3.3 255.255.255.255
!
interface Ethernet0/0
 ip address 192.168.13.3 255.255.255.0

router bgp 1
 network 3.3.3.3 mask 255.255.255.255
 neighbor 192.168.12.2 remote-as 1
 neighbor 192.168.13.1 remote-as 1

ip route 192.168.12.0 255.255.255.0 192.168.13.1

R1#sh ip bgp
BGP table version is 7, local router ID is 192.168.13.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, 
              r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter, 
              x best-external, a additional-path, c RIB-compressed, 
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop            Metric LocPrf Weight Path
 *>i 2.2.2.2/32       192.168.12.2             0    100      0 i
 *>i 3.3.3.3/32       192.168.13.3             0    100      0 i
R1#

R2#show ip bgp 
BGP table version is 3, local router ID is 2.2.2.2
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, 
              r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter, 
              x best-external, a additional-path, c RIB-compressed, 
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop            Metric LocPrf Weight Path
 *>  2.2.2.2/32       0.0.0.0                  0         32768 i
 *>i 3.3.3.3/32       192.168.13.3             0    100      0 i
R2#

R3#sh ip bgp
BGP table version is 3, local router ID is 3.3.3.3
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, 
              r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter, 
              x best-external, a additional-path, c RIB-compressed, 
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop            Metric LocPrf Weight Path
 *>i 2.2.2.2/32       192.168.12.2             0    100      0 i
 *>  3.3.3.3/32       0.0.0.0                  0         32768 i
R3#

R2#ping 3.3.3.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 3.3.3.3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms
R2#

R3#ping 2.2.2.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2.2.2.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms
R3#